1
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Villegas-Aguilar L, Polino E, Ghafari F, Quintino MT, Laverick KT, Berkman IR, Rogge S, Shalm LK, Tischler N, Cavalcanti EG, Slussarenko S, Pryde GJ. Nonlocality activation in a photonic quantum network. Nat Commun 2024; 15:3112. [PMID: 38600084 PMCID: PMC11006907 DOI: 10.1038/s41467-024-47354-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2023] [Accepted: 03/28/2024] [Indexed: 04/12/2024] Open
Abstract
Bell nonlocality refers to correlations between two distant, entangled particles that challenge classical notions of local causality. Beyond its foundational significance, nonlocality is crucial for device-independent technologies like quantum key distribution and randomness generation. Nonlocality quickly deteriorates in the presence of noise, and restoring nonlocal correlations requires additional resources. These often come in the form of many instances of the input state and joint measurements, incurring a significant resource overhead. Here, we experimentally demonstrate that single copies of Bell-local states, incapable of violating any standard Bell inequality, can give rise to nonlocality after being embedded into a quantum network of multiple parties. We subject the initial entangled state to a quantum channel that broadcasts part of the state to two independent receivers and certify the nonlocality in the resulting network by violating a tailored Bell-like inequality. We obtain these results without making any assumptions about the prepared states, the quantum channel, or the validity of quantum theory. Our findings have fundamental implications for nonlocality and enable the practical use of nonlocal correlations in real-world applications, even in scenarios dominated by noise.
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Affiliation(s)
- Luis Villegas-Aguilar
- Centre for Quantum Dynamics and Centre for Quantum Computation and Communication Technology, Griffith University, Yuggera Country, Brisbane, QLD, 4111, Australia
| | - Emanuele Polino
- Centre for Quantum Dynamics and Centre for Quantum Computation and Communication Technology, Griffith University, Yuggera Country, Brisbane, QLD, 4111, Australia
| | - Farzad Ghafari
- Centre for Quantum Dynamics and Centre for Quantum Computation and Communication Technology, Griffith University, Yuggera Country, Brisbane, QLD, 4111, Australia
| | | | - Kiarn T Laverick
- Centre for Quantum Dynamics, Griffith University, Yugambeh Country, Gold Coast, QLD, 4222, Australia
| | - Ian R Berkman
- Centre for Quantum Computation and Communication Technology, School of Physics, The University of New South Wales, Sydney, NSW, 2052, Australia
| | - Sven Rogge
- Centre for Quantum Computation and Communication Technology, School of Physics, The University of New South Wales, Sydney, NSW, 2052, Australia
| | - Lynden K Shalm
- National Institute of Standards and Technology, 325 Broadway, Boulder, CO, 80305, USA
| | - Nora Tischler
- Centre for Quantum Dynamics and Centre for Quantum Computation and Communication Technology, Griffith University, Yuggera Country, Brisbane, QLD, 4111, Australia.
| | - Eric G Cavalcanti
- Centre for Quantum Dynamics, Griffith University, Yugambeh Country, Gold Coast, QLD, 4222, Australia.
| | - Sergei Slussarenko
- Centre for Quantum Dynamics and Centre for Quantum Computation and Communication Technology, Griffith University, Yuggera Country, Brisbane, QLD, 4111, Australia
| | - Geoff J Pryde
- Centre for Quantum Dynamics and Centre for Quantum Computation and Communication Technology, Griffith University, Yuggera Country, Brisbane, QLD, 4111, Australia
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2
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Ghafari F, Tischler N, Di Franco C, Thompson J, Gu M, Pryde GJ. Interfering trajectories in experimental quantum-enhanced stochastic simulation. Nat Commun 2019; 10:1630. [PMID: 30967533 PMCID: PMC6456595 DOI: 10.1038/s41467-019-08951-2] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2018] [Accepted: 02/04/2019] [Indexed: 12/02/2022] Open
Abstract
Simulations of stochastic processes play an important role in the quantitative sciences, enabling the characterisation of complex systems. Recent work has established a quantum advantage in stochastic simulation, leading to quantum devices that execute a simulation using less memory than possible by classical means. To realise this advantage it is essential that the memory register remains coherent, and coherently interacts with the processor, allowing the simulator to operate over many time steps. Here we report a multi-time-step experimental simulation of a stochastic process using less memory than the classical limit. A key feature of the photonic quantum information processor is that it creates a quantum superposition of all possible future trajectories that the system can evolve into. This superposition allows us to introduce, and demonstrate, the idea of comparing statistical futures of two classical processes via quantum interference. We demonstrate interference of two 16-dimensional quantum states, representing statistical futures of our process, with a visibility of 0.96 ± 0.02. Quantum devices should allow simulating stochastic processes using less memory than classical counterparts, but only if quantum coherence is maintained through multiple steps. Here, the authors demonstrate a coherence-preserving three-step stochastic simulation using photons.
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Affiliation(s)
- Farzad Ghafari
- Centre for Quantum Dynamics, Griffith University, Brisbane, QLD, 4111, Australia.
| | - Nora Tischler
- Centre for Quantum Dynamics, Griffith University, Brisbane, QLD, 4111, Australia
| | - Carlo Di Franco
- School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, 639673, Singapore.,Complexity Institute, Nanyang Technological University, Singapore, 639673, Singapore
| | - Jayne Thompson
- Centre for Quantum Technologies, National University of Singapore, Singapore, 117543, Singapore
| | - Mile Gu
- School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, 639673, Singapore. .,Complexity Institute, Nanyang Technological University, Singapore, 639673, Singapore. .,Centre for Quantum Technologies, National University of Singapore, Singapore, 117543, Singapore.
| | - Geoff J Pryde
- Centre for Quantum Dynamics, Griffith University, Brisbane, QLD, 4111, Australia.
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3
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Wei K, Tischler N, Zhao SR, Li YH, Arrazola JM, Liu Y, Zhang W, Li H, You L, Wang Z, Chen YA, Sanders BC, Zhang Q, Pryde GJ, Xu F, Pan JW. Experimental Quantum Switching for Exponentially Superior Quantum Communication Complexity. Phys Rev Lett 2019; 122:120504. [PMID: 30978079 DOI: 10.1103/physrevlett.122.120504] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/23/2018] [Indexed: 06/09/2023]
Abstract
Finding exponential separation between quantum and classical information tasks is like striking gold in quantum information research. Such an advantage is believed to hold for quantum computing but is proven for quantum communication complexity. Recently, a novel quantum resource called the quantum switch-which creates a coherent superposition of the causal order of events, known as quantum causality-has been harnessed theoretically in a new protocol providing provable exponential separation. We experimentally demonstrate such an advantage by realizing a superposition of communication directions for a two-party distributed computation. Our photonic demonstration employs d-dimensional quantum systems, qudits, up to d=2^{13} dimensions and demonstrates a communication complexity advantage, requiring less than (0.696±0.006) times the communication of any causally ordered protocol. These results elucidate the crucial role of the coherence of communication direction in achieving the exponential separation for the one-way processing task, and open a new path for experimentally exploring the fundamentals and applications of advanced features of indefinite causal structures.
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Affiliation(s)
- Kejin Wei
- Shanghai Branch, Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Shanghai 201315, China
- CAS Center for Excellence and Synergetic Innovation Center in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai 201315, China
| | - Nora Tischler
- Centre for Quantum Dynamics, Griffith University, Brisbane QLD 4111, Australia
| | - Si-Ran Zhao
- Shanghai Branch, Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Shanghai 201315, China
- CAS Center for Excellence and Synergetic Innovation Center in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai 201315, China
| | - Yu-Huai Li
- Shanghai Branch, Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Shanghai 201315, China
- CAS Center for Excellence and Synergetic Innovation Center in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai 201315, China
| | - Juan Miguel Arrazola
- Xanadu, 372 Richmond Street W, Toronto, Ontario M5V 1X6, Canada
- Centre for Quantum Technologies, National University of Singapore, 3 Science Drive 2, Singapore 117543
| | - Yang Liu
- Shanghai Branch, Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Shanghai 201315, China
- CAS Center for Excellence and Synergetic Innovation Center in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai 201315, China
| | - Weijun Zhang
- State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
| | - Hao Li
- State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
| | - Lixing You
- State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
| | - Zhen Wang
- State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
| | - Yu-Ao Chen
- Shanghai Branch, Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Shanghai 201315, China
- CAS Center for Excellence and Synergetic Innovation Center in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai 201315, China
| | - Barry C Sanders
- Shanghai Branch, Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Shanghai 201315, China
- Institute for Quantum Science and Technology, University of Calgary, Alberta T2N 1N4, Canada
- Program in Quantum Information Science, Canadian Institute for Advanced Research, Toronto, Ontario M5G 1M1, Canada
| | - Qiang Zhang
- Shanghai Branch, Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Shanghai 201315, China
- CAS Center for Excellence and Synergetic Innovation Center in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai 201315, China
| | - Geoff J Pryde
- Centre for Quantum Dynamics, Griffith University, Brisbane QLD 4111, Australia
| | - Feihu Xu
- Shanghai Branch, Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Shanghai 201315, China
- CAS Center for Excellence and Synergetic Innovation Center in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai 201315, China
| | - Jian-Wei Pan
- Shanghai Branch, Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Shanghai 201315, China
- CAS Center for Excellence and Synergetic Innovation Center in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai 201315, China
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4
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Zhang C, Cheng S, Li L, Liang QY, Liu BH, Huang YF, Li CF, Guo GC, Hall MJW, Wiseman HM, Pryde GJ. Experimental Validation of Quantum Steering Ellipsoids and Tests of Volume Monogamy Relations. Phys Rev Lett 2019; 122:070402. [PMID: 30848627 DOI: 10.1103/physrevlett.122.070402] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/26/2018] [Revised: 01/29/2019] [Indexed: 06/09/2023]
Abstract
The set of all qubit states that can be steered to by measurements on a correlated qubit is predicted to form an ellipsoid-called the quantum steering ellipsoid-in the Bloch ball. This ellipsoid provides a simple visual characterization of the initial two-qubit state, and various aspects of entanglement are reflected in its geometric properties. We experimentally verify these properties via measurements on many different polarization-entangled photonic qubit states. Moreover, for pure three-qubit states, the volumes of the two quantum steering ellipsoids generated by measurements on the first qubit are predicted to satisfy a tight monogamy relation, which is strictly stronger than the well-known monogamy of entanglement for concurrence. We experimentally verify these predictions, using polarization and path entanglement. We also show experimentally that this monogamy relation can be violated by a mixed entangled state, which nevertheless satisfies a weaker monogamy relation.
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Affiliation(s)
- Chao Zhang
- Key Laboratory of Quantum Information, University of Science and Technology of China, CAS, Hefei 230026, People's Republic of China
- CAS Center For Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, People's Republic of China
| | - Shuming Cheng
- Centre for Quantum Computation and Communication Technology (Australian Research Council), Centre for Quantum Dynamics, Griffith University, Brisbane QLD 4111, Australia
| | - Li Li
- Centre for Quantum Computation and Communication Technology (Australian Research Council), Centre for Quantum Dynamics, Griffith University, Brisbane QLD 4111, Australia
| | - Qiu-Yue Liang
- Key Laboratory of Quantum Information, University of Science and Technology of China, CAS, Hefei 230026, People's Republic of China
- CAS Center For Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, People's Republic of China
| | - Bi-Heng Liu
- Key Laboratory of Quantum Information, University of Science and Technology of China, CAS, Hefei 230026, People's Republic of China
- CAS Center For Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, People's Republic of China
| | - Yun-Feng Huang
- Key Laboratory of Quantum Information, University of Science and Technology of China, CAS, Hefei 230026, People's Republic of China
- CAS Center For Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, People's Republic of China
| | - Chuan-Feng Li
- Key Laboratory of Quantum Information, University of Science and Technology of China, CAS, Hefei 230026, People's Republic of China
- CAS Center For Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, People's Republic of China
| | - Guang-Can Guo
- Key Laboratory of Quantum Information, University of Science and Technology of China, CAS, Hefei 230026, People's Republic of China
- CAS Center For Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, People's Republic of China
| | - Michael J W Hall
- Centre for Quantum Computation and Communication Technology (Australian Research Council), Centre for Quantum Dynamics, Griffith University, Brisbane QLD 4111, Australia
| | - Howard M Wiseman
- Centre for Quantum Computation and Communication Technology (Australian Research Council), Centre for Quantum Dynamics, Griffith University, Brisbane QLD 4111, Australia
| | - Geoff J Pryde
- Centre for Quantum Computation and Communication Technology (Australian Research Council), Centre for Quantum Dynamics, Griffith University, Brisbane QLD 4111, Australia
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5
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Pepper A, Tischler N, Pryde GJ. Experimental Realization of a Quantum Autoencoder: The Compression of Qutrits via Machine Learning. Phys Rev Lett 2019; 122:060501. [PMID: 30822053 DOI: 10.1103/physrevlett.122.060501] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/05/2018] [Indexed: 06/09/2023]
Abstract
With quantum resources a precious commodity, their efficient use is highly desirable. Quantum autoencoders have been proposed as a way to reduce quantum memory requirements. Generally, an autoencoder is a device that uses machine learning to compress inputs, that is, to represent the input data in a lower-dimensional space. Here, we experimentally realize a quantum autoencoder, which learns how to compress quantum data using a classical optimization routine. We demonstrate that when the inherent structure of the dataset allows lossless compression, our autoencoder reduces qutrits to qubits with low error levels. We also show that the device is able to perform with minimal prior information about the quantum data or physical system and is robust to perturbations during its optimization routine.
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Affiliation(s)
- Alex Pepper
- Centre for Quantum Dynamics, Griffith University, Brisbane, QLD 4111, Australia
| | - Nora Tischler
- Centre for Quantum Dynamics, Griffith University, Brisbane, QLD 4111, Australia
| | - Geoff J Pryde
- Centre for Quantum Dynamics, Griffith University, Brisbane, QLD 4111, Australia
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6
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Abstract
There has been a concerted effort to identify problems computable with quantum technology, which are intractable with classical technology or require far fewer resources to compute. Recently, randomness processing in a Bernoulli factory has been identified as one such task. Here, we report two quantum photonic implementations of a Bernoulli factory, one using quantum coherence and single-qubit measurements and the other one using quantum coherence and entangling measurements of two qubits. We show that the former consumes three orders of magnitude fewer resources than the best-known classical method, while entanglement offers a further fivefold reduction. These concepts may provide a means for quantum-enhanced performance in the simulation of stochastic processes and sampling tasks.
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Affiliation(s)
- Raj B. Patel
- Centre for Quantum Computation and Communication Technology and Centre for Quantum Dynamics, Griffith University, Brisbane 4111, Australia
| | - Terry Rudolph
- Department of Physics, Imperial College London, Prince Consort Road, London SW7 2AZ, UK
| | - Geoff J. Pryde
- Centre for Quantum Computation and Communication Technology and Centre for Quantum Dynamics, Griffith University, Brisbane 4111, Australia
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7
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Tischler N, Ghafari F, Baker TJ, Slussarenko S, Patel RB, Weston MM, Wollmann S, Shalm LK, Verma VB, Nam SW, Nguyen HC, Wiseman HM, Pryde GJ. Conclusive Experimental Demonstration of One-Way Einstein-Podolsky-Rosen Steering. Phys Rev Lett 2018; 121:100401. [PMID: 30240270 DOI: 10.1103/physrevlett.121.100401] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/31/2018] [Revised: 08/02/2018] [Indexed: 06/08/2023]
Abstract
Einstein-Podolsky-Rosen steering is a quantum phenomenon wherein one party influences, or steers, the state of a distant party's particle beyond what could be achieved with a separable state, by making measurements on one-half of an entangled state. This type of quantum nonlocality stands out through its asymmetric setting and even allows for cases where one party can steer the other but where the reverse is not true. A series of experiments have demonstrated one-way steering in the past, but all were based on significant limiting assumptions. These consisted either of restrictions on the type of allowed measurements or of assumptions about the quantum state at hand, by mapping to a specific family of states and analyzing the ideal target state rather than the real experimental state. Here, we present the first experimental demonstration of one-way steering free of such assumptions. We achieve this using a new sufficient condition for nonsteerability and, although not required by our analysis, using a novel source of extremely high-quality photonic Werner states.
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Affiliation(s)
- Nora Tischler
- Centre for Quantum Computation and Communication Technology (Australian Research Council), Centre for Quantum Dynamics, Griffith University, Brisbane, Queensland 4111, Australia
| | - Farzad Ghafari
- Centre for Quantum Computation and Communication Technology (Australian Research Council), Centre for Quantum Dynamics, Griffith University, Brisbane, Queensland 4111, Australia
| | - Travis J Baker
- Centre for Quantum Computation and Communication Technology (Australian Research Council), Centre for Quantum Dynamics, Griffith University, Brisbane, Queensland 4111, Australia
| | - Sergei Slussarenko
- Centre for Quantum Computation and Communication Technology (Australian Research Council), Centre for Quantum Dynamics, Griffith University, Brisbane, Queensland 4111, Australia
| | - Raj B Patel
- Centre for Quantum Computation and Communication Technology (Australian Research Council), Centre for Quantum Dynamics, Griffith University, Brisbane, Queensland 4111, Australia
- Centre for Quantum Computation and Communication Technology (Australian Research Council), Quantum Photonics Laboratory, School of Engineering, RMIT University, Melbourne, Victoria 3000, Australia
| | - Morgan M Weston
- Centre for Quantum Computation and Communication Technology (Australian Research Council), Centre for Quantum Dynamics, Griffith University, Brisbane, Queensland 4111, Australia
| | - Sabine Wollmann
- Centre for Quantum Computation and Communication Technology (Australian Research Council), Centre for Quantum Dynamics, Griffith University, Brisbane, Queensland 4111, Australia
- Quantum Engineering Technology Labs, H. H. Wills Physics Laboratory and Department of Electrical and Electronic Engineering, University of Bristol, Bristol BS8 1FD, United Kingdom
| | - Lynden K Shalm
- National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305, USA
| | - Varun B Verma
- National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305, USA
| | - Sae Woo Nam
- National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305, USA
| | - H Chau Nguyen
- Naturwissenschaftlich-Technische Fakultät, Universität Siegen, Walter-Flex-Straße 3, D-57068 Siegen, Germany
| | - Howard M Wiseman
- Centre for Quantum Computation and Communication Technology (Australian Research Council), Centre for Quantum Dynamics, Griffith University, Brisbane, Queensland 4111, Australia
| | - Geoff J Pryde
- Centre for Quantum Computation and Communication Technology (Australian Research Council), Centre for Quantum Dynamics, Griffith University, Brisbane, Queensland 4111, Australia
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8
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Bong KW, Tischler N, Patel RB, Wollmann S, Pryde GJ, Hall MJW. Strong Unitary and Overlap Uncertainty Relations: Theory and Experiment. Phys Rev Lett 2018; 120:230402. [PMID: 29932718 DOI: 10.1103/physrevlett.120.230402] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/21/2017] [Revised: 12/18/2017] [Indexed: 06/08/2023]
Abstract
We derive and experimentally investigate a strong uncertainty relation valid for any n unitary operators, which implies the standard uncertainty relation and others as special cases, and which can be written in terms of geometric phases. It is saturated by every pure state of any n-dimensional quantum system, generates a tight overlap uncertainty relation for the transition probabilities of any n+1 pure states, and gives an upper bound for the out-of-time-order correlation function. We test these uncertainty relations experimentally for photonic polarization qubits, including the minimum uncertainty states of the overlap uncertainty relation, via interferometric measurements of generalized geometric phases.
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Affiliation(s)
- Kok-Wei Bong
- Centre for Quantum Computation and Communication Technology (Australian Research Council), Centre for Quantum Dynamics, Griffith University, Brisbane QLD 4111, Australia
| | - Nora Tischler
- Centre for Quantum Computation and Communication Technology (Australian Research Council), Centre for Quantum Dynamics, Griffith University, Brisbane QLD 4111, Australia
| | - Raj B Patel
- Centre for Quantum Computation and Communication Technology (Australian Research Council), Centre for Quantum Dynamics, Griffith University, Brisbane QLD 4111, Australia
| | - Sabine Wollmann
- Centre for Quantum Computation and Communication Technology (Australian Research Council), Centre for Quantum Dynamics, Griffith University, Brisbane QLD 4111, Australia
- Quantum Engineering Technology Labs, H. H. Wills Physics Laboratory and Department of Electrical and Electronic Engineering, University of Bristol, Bristol BS8 1FD, United Kingdom
| | - Geoff J Pryde
- Centre for Quantum Computation and Communication Technology (Australian Research Council), Centre for Quantum Dynamics, Griffith University, Brisbane QLD 4111, Australia
| | - Michael J W Hall
- Centre for Quantum Computation and Communication Technology (Australian Research Council), Centre for Quantum Dynamics, Griffith University, Brisbane QLD 4111, Australia
- Department of Theoretical Physics, Research School of Physics and Engineering, Australian National University, Canberra ACT 0200, Australia
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9
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Weston MM, Slussarenko S, Chrzanowski HM, Wollmann S, Shalm LK, Verma VB, Allman MS, Nam SW, Pryde GJ. Heralded quantum steering over a high-loss channel. Sci Adv 2018; 4:e1701230. [PMID: 29322093 PMCID: PMC5756093 DOI: 10.1126/sciadv.1701230] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/18/2017] [Accepted: 11/20/2017] [Indexed: 05/20/2023]
Abstract
Entanglement is the key resource for many long-range quantum information tasks, including secure communication and fundamental tests of quantum physics. These tasks require robust verification of shared entanglement, but performing it over long distances is presently technologically intractable because the loss through an optical fiber or free-space channel opens up a detection loophole. We design and experimentally demonstrate a scheme that verifies entanglement in the presence of at least 14.8 ± 0.1 dB of added loss, equivalent to approximately 80 km of telecommunication fiber. Our protocol relies on entanglement swapping to herald the presence of a photon after the lossy channel, enabling event-ready implementation of quantum steering. This result overcomes the key barrier in device-independent communication under realistic high-loss scenarios and in the realization of a quantum repeater.
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Affiliation(s)
- Morgan M. Weston
- Centre for Quantum Dynamics and Centre for Quantum Computation and Communication Technology, Griffith University, Brisbane, Queensland 4111, Australia
| | - Sergei Slussarenko
- Centre for Quantum Dynamics and Centre for Quantum Computation and Communication Technology, Griffith University, Brisbane, Queensland 4111, Australia
| | - Helen M. Chrzanowski
- Centre for Quantum Dynamics and Centre for Quantum Computation and Communication Technology, Griffith University, Brisbane, Queensland 4111, Australia
- Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, UK
| | - Sabine Wollmann
- Centre for Quantum Dynamics and Centre for Quantum Computation and Communication Technology, Griffith University, Brisbane, Queensland 4111, Australia
- Quantum Engineering Technology Labs, H. H. Wills Physics Laboratory and Department of Electrical and Electronic Engineering, University of Bristol, BS8 1FD, UK
| | - Lynden K. Shalm
- National Institute of Standards and Technology, 325 Broadway, Boulder, CO 80305, USA
| | - Varun B. Verma
- National Institute of Standards and Technology, 325 Broadway, Boulder, CO 80305, USA
| | - Michael S. Allman
- National Institute of Standards and Technology, 325 Broadway, Boulder, CO 80305, USA
| | - Sae Woo Nam
- National Institute of Standards and Technology, 325 Broadway, Boulder, CO 80305, USA
| | - Geoff J. Pryde
- Centre for Quantum Dynamics and Centre for Quantum Computation and Communication Technology, Griffith University, Brisbane, Queensland 4111, Australia
- Corresponding author.
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10
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Slussarenko S, Weston MM, Li JG, Campbell N, Wiseman HM, Pryde GJ. Erratum: Quantum State Discrimination Using the Minimum Average Number of Copies [Phys. Rev. Lett. 118, 030502 (2017)]. Phys Rev Lett 2017; 118:259901. [PMID: 28696760 DOI: 10.1103/physrevlett.118.259901] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2017] [Indexed: 06/07/2023]
Abstract
This corrects the article DOI: 10.1103/PhysRevLett.118.030502.
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11
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Saunders DJ, Bennet AJ, Branciard C, Pryde GJ. Experimental demonstration of nonbilocal quantum correlations. Sci Adv 2017; 3:e1602743. [PMID: 28508045 PMCID: PMC5409499 DOI: 10.1126/sciadv.1602743] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/06/2016] [Accepted: 02/14/2017] [Indexed: 05/07/2023]
Abstract
Quantum mechanics admits correlations that cannot be explained by local realistic models. The most studied models are the standard local hidden variable models, which satisfy the well-known Bell inequalities. To date, most works have focused on bipartite entangled systems. We consider correlations between three parties connected via two independent entangled states. We investigate the new type of so-called "bilocal" models, which correspondingly involve two independent hidden variables. These models describe scenarios that naturally arise in quantum networks, where several independent entanglement sources are used. Using photonic qubits, we build such a linear three-node quantum network and demonstrate nonbilocal correlations by violating a Bell-like inequality tailored for bilocal models. Furthermore, we show that the demonstration of nonbilocality is more noise-tolerant than that of standard Bell nonlocality in our three-party quantum network.
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Affiliation(s)
- Dylan J. Saunders
- Centre for Quantum Dynamics and Centre for Quantum Computation and Communication Technology, Griffith University, Brisbane, Queensland 4111, Australia
- Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, U.K
| | - Adam J. Bennet
- Centre for Quantum Dynamics and Centre for Quantum Computation and Communication Technology, Griffith University, Brisbane, Queensland 4111, Australia
| | - Cyril Branciard
- Institut Néel, CNRS and Université Grenoble Alpes, 38042 Grenoble Cedex 9, France
| | - Geoff J. Pryde
- Centre for Quantum Dynamics and Centre for Quantum Computation and Communication Technology, Griffith University, Brisbane, Queensland 4111, Australia
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12
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Palsson MS, Gu M, Ho J, Wiseman HM, Pryde GJ. Experimentally modeling stochastic processes with less memory by the use of a quantum processor. Sci Adv 2017; 3:e1601302. [PMID: 28168218 PMCID: PMC5291701 DOI: 10.1126/sciadv.1601302] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2016] [Accepted: 12/22/2016] [Indexed: 05/30/2023]
Abstract
Computer simulation of observable phenomena is an indispensable tool for engineering new technology, understanding the natural world, and studying human society. However, the most interesting systems are often so complex that simulating their future behavior demands storing immense amounts of information regarding how they have behaved in the past. For increasingly complex systems, simulation becomes increasingly difficult and is ultimately constrained by resources such as computer memory. Recent theoretical work shows that quantum theory can reduce this memory requirement beyond ultimate classical limits, as measured by a process' statistical complexity, C. We experimentally demonstrate this quantum advantage in simulating stochastic processes. Our quantum implementation observes a memory requirement of Cq = 0.05 ± 0.01, far below the ultimate classical limit of C = 1. Scaling up this technique would substantially reduce the memory required in simulations of more complex systems.
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Affiliation(s)
- Matthew S. Palsson
- Centre for Quantum Computation and Communication Technology (Australian Research Council), Centre for Quantum Dynamics, Griffith University, Brisbane, Queensland 4111, Australia
| | - Mile Gu
- School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 639673, Republic of Singapore
- Complexity Institute, Nanyang Technological University, 60 Nanyang View, Singapore 639673, Republic of Singapore
- Centre for Quantum Technologies, National University of Singapore, 3 Science Drive 2, Singapore, Republic of Singapore
| | - Joseph Ho
- Centre for Quantum Computation and Communication Technology (Australian Research Council), Centre for Quantum Dynamics, Griffith University, Brisbane, Queensland 4111, Australia
| | - Howard M. Wiseman
- Centre for Quantum Computation and Communication Technology (Australian Research Council), Centre for Quantum Dynamics, Griffith University, Brisbane, Queensland 4111, Australia
| | - Geoff J. Pryde
- Centre for Quantum Computation and Communication Technology (Australian Research Council), Centre for Quantum Dynamics, Griffith University, Brisbane, Queensland 4111, Australia
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13
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Slussarenko S, Weston MM, Li JG, Campbell N, Wiseman HM, Pryde GJ. Quantum State Discrimination Using the Minimum Average Number of Copies. Phys Rev Lett 2017; 118:030502. [PMID: 28157368 DOI: 10.1103/physrevlett.118.030502] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/25/2016] [Indexed: 06/06/2023]
Abstract
In the task of discriminating between nonorthogonal quantum states from multiple copies, the key parameters are the error probability and the resources (number of copies) used. Previous studies have considered the task of minimizing the average error probability for fixed resources. Here we introduce a new state discrimination task: minimizing the average resources for a fixed admissible error probability. We show that this new task is not performed optimally by previously known strategies, and derive and experimentally test a detection scheme that performs better.
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Affiliation(s)
- Sergei Slussarenko
- Centre for Quantum Dynamics and Centre for Quantum Computation and Communication Technology, Griffith University, Brisbane, Queensland 4111, Australia
| | - Morgan M Weston
- Centre for Quantum Dynamics and Centre for Quantum Computation and Communication Technology, Griffith University, Brisbane, Queensland 4111, Australia
| | - Jun-Gang Li
- Centre for Quantum Dynamics and Centre for Quantum Computation and Communication Technology, Griffith University, Brisbane, Queensland 4111, Australia
- School of Physics, Beijing Institute of Technology, Beijing 100081, China
| | - Nicholas Campbell
- Centre for Quantum Dynamics and Centre for Quantum Computation and Communication Technology, Griffith University, Brisbane, Queensland 4111, Australia
| | - Howard M Wiseman
- Centre for Quantum Dynamics and Centre for Quantum Computation and Communication Technology, Griffith University, Brisbane, Queensland 4111, Australia
| | - Geoff J Pryde
- Centre for Quantum Dynamics and Centre for Quantum Computation and Communication Technology, Griffith University, Brisbane, Queensland 4111, Australia
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14
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Weston MM, Chrzanowski HM, Wollmann S, Boston A, Ho J, Shalm LK, Verma VB, Allman MS, Nam SW, Patel RB, Slussarenko S, Pryde GJ. Efficient and pure femtosecond-pulse-length source of polarization-entangled photons. Opt Express 2016; 24:10869-10879. [PMID: 27409907 DOI: 10.1364/oe.24.010869] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
We present a source of polarization entangled photon pairs based on spontaneous parametric downconversion engineered for frequency uncorrelated telecom photon generation. Our source provides photon pairs that display, simultaneously, the key properties for high-performance quantum information and fundamental quantum science tasks. Specifically, the source provides for high heralding efficiency, high quantum state purity and high entangled state fidelity at the same time. Among different tests we apply to our source we observe almost perfect non-classical interference between photons from independent sources with a visibility of (100 ± 5)%.
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15
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Wollmann S, Walk N, Bennet AJ, Wiseman HM, Pryde GJ. Observation of Genuine One-Way Einstein-Podolsky-Rosen Steering. Phys Rev Lett 2016; 116:160403. [PMID: 27152777 DOI: 10.1103/physrevlett.116.160403] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/03/2015] [Indexed: 06/05/2023]
Abstract
Within the hierarchy of inseparable quantum correlations, Einstein-Podolsky-Rosen steering is distinguished from both entanglement and Bell nonlocality by its asymmetry-there exist conditions where the steering phenomenon changes from being observable to not observable, simply by exchanging the role of the two measuring parties. While this one-way steering feature has been previously demonstrated for the restricted class of Gaussian measurements, for the general case of positive-operator-valued measures even its theoretical existence has only recently been settled. Here, we prove, and then experimentally observe, the one-way steerability of an experimentally practical class of entangled states in this general setting. As well as its foundational significance, the demonstration of fundamentally asymmetric nonlocality also has practical implications for the distribution of the trust in quantum communication networks.
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Affiliation(s)
- Sabine Wollmann
- Centre for Quantum Computation and Communication Technology and Centre for Quantum Dynamics, Griffith University, Brisbane, Queensland 4111, Australia
| | - Nathan Walk
- Centre for Quantum Computation and Communication Technology and Centre for Quantum Dynamics, Griffith University, Brisbane, Queensland 4111, Australia
- Department of Computer Science, University of Oxford, Oxford OX1 3QD, United Kingdom
| | - Adam J Bennet
- Centre for Quantum Computation and Communication Technology and Centre for Quantum Dynamics, Griffith University, Brisbane, Queensland 4111, Australia
| | - Howard M Wiseman
- Centre for Quantum Computation and Communication Technology and Centre for Quantum Dynamics, Griffith University, Brisbane, Queensland 4111, Australia
| | - Geoff J Pryde
- Centre for Quantum Computation and Communication Technology and Centre for Quantum Dynamics, Griffith University, Brisbane, Queensland 4111, Australia
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16
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Abstract
Minimizing the resources required to build logic gates into useful processing circuits is key to realizing quantum computers. Although the salient features of a quantum computer have been shown in proof-of-principle experiments, difficulties in scaling quantum systems have made more complex operations intractable. This is exemplified in the classical Fredkin (controlled-SWAP) gate for which, despite theoretical proposals, no quantum analog has been realized. By adding control to the SWAP unitary, we use photonic qubit logic to demonstrate the first quantum Fredkin gate, which promises many applications in quantum information and measurement. We implement example algorithms and generate the highest-fidelity three-photon Greenberger-Horne-Zeilinger states to date. The technique we use allows one to add a control operation to a black-box unitary, something that is impossible in the standard circuit model. Our experiment represents the first use of this technique to control a two-qubit operation and paves the way for larger controlled circuits to be realized efficiently.
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Affiliation(s)
- Raj B. Patel
- CQCT (Centre for Quantum Computation & Communication Technology) and Centre for Quantum Dynamics, Griffith University, Brisbane 4111, Australia
- Corresponding author. E-mail: (R.B.P.); (G.J.P.)
| | - Joseph Ho
- CQCT (Centre for Quantum Computation & Communication Technology) and Centre for Quantum Dynamics, Griffith University, Brisbane 4111, Australia
| | - Franck Ferreyrol
- CQCT (Centre for Quantum Computation & Communication Technology) and Centre for Quantum Dynamics, Griffith University, Brisbane 4111, Australia
- Laboratoire Photonique, Numerique et Nanosciences, Institut d’Optique, CNRS and Université de Bordeaux, 33400 Talence, France
| | - Timothy C. Ralph
- CQCT and School of Mathematics and Physics, University of Queensland, Brisbane 4072, Australia
| | - Geoff J. Pryde
- CQCT (Centre for Quantum Computation & Communication Technology) and Centre for Quantum Dynamics, Griffith University, Brisbane 4111, Australia
- Corresponding author. E-mail: (R.B.P.); (G.J.P.)
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17
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Bennet A, Vértesi T, Saunders DJ, Brunner N, Pryde GJ. Experimental semi-device-independent certification of entangled measurements. Phys Rev Lett 2014; 113:080405. [PMID: 25192081 DOI: 10.1103/physrevlett.113.080405] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/03/2014] [Indexed: 06/03/2023]
Abstract
Certifying the entanglement of quantum states with Bell inequalities allows one to guarantee the security of quantum information protocols independently of imperfections in the measuring devices. Here, we present a similar procedure for witnessing entangled measurements, which play a central role in many quantum information tasks. Our procedure is termed semi-device-independent, as it uses uncharacterized quantum preparations of fixed Hilbert space dimension. Using a photonic setup, we experimentally certify an entangled measurement using only measurement statistics. We also apply our techniques to certify unentangled but nevertheless inherently quantum measurements.
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Affiliation(s)
- Adam Bennet
- Centre for Quantum Dynamics and Centre for Quantum Computation and Communication Technology, Griffith University, Brisbane, Queensland 4111, Australia
| | - Tamás Vértesi
- Institute for Nuclear Research, Hungarian Academy of Sciences, P.O. Box 51, H-4001 Debrecen, Hungary
| | - Dylan J Saunders
- Centre for Quantum Dynamics and Centre for Quantum Computation and Communication Technology, Griffith University, Brisbane, Queensland 4111, Australia and Clarendon Laboratory, Department of Physics, University of Oxford, Oxford OX1 3PU, United Kingdom
| | - Nicolas Brunner
- Département de Physique Théorique, Université de Genève, 1211 Genève, Switzerland
| | - G J Pryde
- Centre for Quantum Dynamics and Centre for Quantum Computation and Communication Technology, Griffith University, Brisbane, Queensland 4111, Australia
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18
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Abstract
Quantum entanglement can help to increase the precision of optical phase measurements beyond the shot noise limit (SNL) to the ultimate Heisenberg limit. However, the N-photon parity measurements required to achieve this optimal sensitivity are extremely difficult to realize with current photon detection technologies, requiring high-fidelity resolution of N + 1 different photon distributions between the output ports. Recent experimental demonstrations of precision beyond the SNL have therefore used only one or two photon-number detection patterns instead of parity measurements. Here we investigate the achievable phase sensitivity of the simple and efficient single interference fringe detection technique. We show that the maximally-entangled "NOON" state does not achieve optimal phase sensitivity when N > 4, rather, we show that the Holland-Burnett state is optimal. We experimentally demonstrate this enhanced sensitivity using a single photon-counted fringe of the six-photon Holland-Burnett state. Specifically, our single-fringe six-photon measurement achieves a phase variance three times below the SNL.
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Affiliation(s)
- G Y Xiang
- 1] Centre for Quantum Dynamics and Centre for Quantum Computation and Communication Technology, Griffith University, Brisbane, 4111, Australia [2] Key Laboratory of Quantum Information, University of Science and Technology of China, CAS, Hefei 230026, China
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19
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Weston MM, Hall MJW, Palsson MS, Wiseman HM, Pryde GJ. Experimental test of universal complementarity relations. Phys Rev Lett 2013; 110:220402. [PMID: 23767702 DOI: 10.1103/physrevlett.110.220402] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/29/2012] [Revised: 03/23/2013] [Indexed: 06/02/2023]
Abstract
Complementarity restricts the accuracy with which incompatible quantum observables can be jointly measured. Despite popular conception, the Heisenberg uncertainty relation does not quantify this principle. We report the experimental verification of universally valid complementarity relations, including an improved relation derived here. We exploit Einstein-Poldolsky-Rosen correlations between two photonic qubits to jointly measure incompatible observables of one. The product of our measurement inaccuracies is low enough to violate the widely used, but not universally valid, Arthurs-Kelly relation.
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Affiliation(s)
- Morgan M Weston
- Centre for Quantum Computation and Communication Technology (Australian Research Council), Centre for Quantum Dynamics, Griffith University, Brisbane QLD 4111, Australia
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20
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Gillett GG, Dalton RB, Lanyon BP, Almeida MP, Barbieri M, Pryde GJ, O'Brien JL, Resch KJ, Bartlett SD, White AG. Experimental feedback control of quantum systems using weak measurements. Phys Rev Lett 2010; 104:080503. [PMID: 20366921 DOI: 10.1103/physrevlett.104.080503] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/24/2009] [Indexed: 05/29/2023]
Abstract
A goal of the emerging field of quantum control is to develop methods for quantum technologies to function robustly in the presence of noise. Central issues are the fundamental limitations on the available information about quantum systems and the disturbance they suffer in the process of measurement. In the context of a simple quantum control scenario-the stabilization of nonorthogonal states of a qubit against dephasing-we experimentally explore the use of weak measurements in feedback control. We find that, despite the intrinsic difficultly of implementing them, weak measurements allow us to control the qubit better in practice than is even theoretically possible without them. Our work shows that these more general quantum measurements can play an important role for feedback control of quantum systems.
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Affiliation(s)
- G G Gillett
- Department of Physics and Centre for Quantum Computer Technology, The University of Queensland, Brisbane 4072, Australia.
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21
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Higgins BL, Booth BM, Doherty AC, Bartlett SD, Wiseman HM, Pryde GJ. Mixed state discrimination using optimal control. Phys Rev Lett 2009; 103:220503. [PMID: 20366079 DOI: 10.1103/physrevlett.103.220503] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/07/2009] [Indexed: 05/29/2023]
Abstract
We present theory and experiment for the task of discriminating two nonorthogonal states, given multiple copies. We implement several local measurement schemes, on both pure states and states mixed by depolarizing noise. We find that schemes which are optimal (or have optimal scaling) without noise perform worse with noise than simply repeating the optimal single-copy measurement. Applying optimal control theory, we derive the globally optimal local measurement strategy, which outperforms all other local schemes, and experimentally implement it for various levels of noise.
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Affiliation(s)
- B L Higgins
- Centre for Quantum Dynamics, Griffith University, Brisbane, 4111, Australia
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22
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Spekkens RW, Buzacott DH, Keehn AJ, Toner B, Pryde GJ. Preparation contextuality powers parity-oblivious multiplexing. Phys Rev Lett 2009; 102:010401. [PMID: 19257170 DOI: 10.1103/physrevlett.102.010401] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/12/2008] [Indexed: 05/27/2023]
Abstract
In a noncontextual hidden variable model of quantum theory, hidden variables determine the outcomes of every measurement in a manner that is independent of how the measurement is implemented. Using a generalization of this notion to arbitrary operational theories and to preparation procedures, we demonstrate that a particular two-party information-processing task, "parity-oblivious multiplexing," is powered by contextuality in the sense that there is a limit to how well any theory described by a noncontextual hidden variable model can perform. This bound constitutes a "noncontextuality inequality" that is violated by quantum theory. We report an experimental violation of this inequality in good agreement with the quantum predictions. The experimental results also provide the first demonstration of 2-to-1 and 3-to-1 quantum random access codes.
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23
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Pryde GJ. Quantum physics: Squeeze until it hurts. Nature 2009; 457:35-6. [PMID: 19122628 DOI: 10.1038/457035a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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24
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Resch KJ, Pregnell KL, Prevedel R, Gilchrist A, Pryde GJ, O'Brien JL, White AG. Time-reversal and super-resolving phase measurements. Phys Rev Lett 2007; 98:223601. [PMID: 17677842 DOI: 10.1103/physrevlett.98.223601] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/07/2006] [Indexed: 05/16/2023]
Abstract
We demonstrate phase super-resolution in the absence of entangled states. The key insight is to use the inherent time-reversal symmetry of quantum mechanics: our theory shows that it is possible to measure, as opposed to prepare, entangled states. Our approach is robust, requiring only photons that exhibit classical interference: we experimentally demonstrate high-visibility phase super-resolution with three, four, and six photons using a standard laser and photon counters. Our six-photon experiment demonstrates the best phase super-resolution yet reported with high visibility and resolution.
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Affiliation(s)
- K J Resch
- Department of Physics, University of Queensland, Brisbane QLD 4072, Australia
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25
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Langford NK, Weinhold TJ, Prevedel R, Resch KJ, Gilchrist A, O'Brien JL, Pryde GJ, White AG. Demonstration of a simple entangling optical gate and its use in bell-state analysis. Phys Rev Lett 2005; 95:210504. [PMID: 16384124 DOI: 10.1103/physrevlett.95.210504] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2005] [Indexed: 05/05/2023]
Abstract
We demonstrate a new architecture for an optical entangling gate that is significantly simpler than previous realizations, using partially polarizing beam splitters so that only a single optical mode-matching condition is required. We demonstrate operation of a controlled-z gate in both continuous-wave and pulsed regimes of operation, fully characterizing it in each case using quantum process tomography. We also demonstrate a fully resolving, nondeterministic optical Bell-state analyzer based on this controlled-z gate. This new architecture is ideally suited to guided optics implementations of optical gates.
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Affiliation(s)
- N K Langford
- Centre for Quantum Computer Technology, University of Queensland, Brisbane QLD 4072, Australia
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26
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Pryde GJ, O'Brien JL, White AG, Ralph TC, Wiseman HM. Measurement of quantum weak values of photon polarization. Phys Rev Lett 2005; 94:220405. [PMID: 16090372 DOI: 10.1103/physrevlett.94.220405] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/27/2004] [Indexed: 05/03/2023]
Abstract
We experimentally determine weak values for a single photon's polarization, obtained via a weak measurement that employs a two-photon entangling operation, and postselection. The weak values cannot be explained by a semiclassical wave theory, due to the two-photon entanglement. We observe the variation in the size of the weak value with measurement strength, obtaining an average measurement of the S1 Stokes parameter more than an order of magnitude outside of the operator's spectrum for the smallest measurement strengths.
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Affiliation(s)
- G J Pryde
- Centre for Quantum Computer Technology, Physics Department, The University of Queensland, Brisbane, Queensland 4072, Australia
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27
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Pryde GJ, O'Brien JL, White AG, Bartlett SD. Demonstrating superior discrimination of locally prepared states using nonlocal measurements. Phys Rev Lett 2005; 94:220406. [PMID: 16090373 DOI: 10.1103/physrevlett.94.220406] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/25/2004] [Indexed: 05/03/2023]
Abstract
We experimentally demonstrate the superior discrimination of separated, unentangled two-qubit correlated states using nonlocal measurements, when compared with measurements based on local operations and classical communications. When predicted theoretically, this phenomenon was dubbed "quantum nonlocality without entanglement." We characterize the performance of the nonlocal, or joint, measurement with a payoff function, for which we measure 0.72 +/- 0.02, compared with the maximum locally achievable value of 2/3 and the overall optimal value of 0.75.
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Affiliation(s)
- G J Pryde
- Centre for Quantum Computer Technology, Physics Department, The University of Queensland, Brisbane 4072, Australia
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28
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O'Brien JL, Pryde GJ, Gilchrist A, James DFV, Langford NK, Ralph TC, White AG. Quantum process tomography of a controlled-NOT gate. Phys Rev Lett 2004; 93:080502. [PMID: 15447165 DOI: 10.1103/physrevlett.93.080502] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/29/2004] [Indexed: 05/24/2023]
Abstract
We demonstrate complete characterization of a two-qubit entangling process--a linear optics controlled-NOT gate operating with coincident detection--by quantum process tomography. We use a maximum-likelihood estimation to convert the experimental data into a physical process matrix. The process matrix allows an accurate prediction of the operation of the gate for arbitrary input states and a calculation of gate performance measures such as the average gate fidelity, average purity, and entangling capability of our gate, which are 0.90, 0.83, and 0.73, respectively.
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Affiliation(s)
- J L O'Brien
- Centre for Quantum Computer Technology and Physics Department, University of Queensland, Brisbane 4072, Australia
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29
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Langford NK, Dalton RB, Harvey MD, O'Brien JL, Pryde GJ, Gilchrist A, Bartlett SD, White AG. Measuring entangled qutrits and their use for quantum bit commitment. Phys Rev Lett 2004; 93:053601. [PMID: 15323694 DOI: 10.1103/physrevlett.93.053601] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2003] [Indexed: 05/14/2023]
Abstract
We produce and holographically measure entangled qudits encoded in transverse spatial modes of single photons. With the novel use of a quantum state tomography method that only requires two-state superpositions, we achieve the most complete characterization of entangled qutrits to date. Ideally, entangled qutrits provide better security than qubits in quantum bit commitment: we model the sensitivity of this to mixture and show experimentally and theoretically that qutrits with even a small amount of decoherence cannot offer increased security over qubits.
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Affiliation(s)
- N K Langford
- Department of Physics, University of Queensland, Brisbane, QLD 4072, Australia
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30
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Pryde GJ, O'Brien JL, White AG, Bartlett SD, Ralph TC. Measuring a photonic qubit without destroying it. Phys Rev Lett 2004; 92:190402. [PMID: 15169391 DOI: 10.1103/physrevlett.92.190402] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/05/2003] [Indexed: 05/24/2023]
Abstract
Measuring the polarization of a single photon typically results in its destruction. We propose, demonstrate, and completely characterize a quantum nondemolition (QND) scheme for realizing such a measurement nondestructively. This scheme uses only linear optics and photodetection of ancillary modes to induce a strong nonlinearity at the single-photon level, nondeterministically. We vary this QND measurement continuously into the weak regime and use it to perform a nondestructive test of complementarity in quantum mechanics. Our scheme realizes the most advanced general measurement of a qubit to date: it is nondestructive, can be made in any basis, and with arbitrary strength.
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Affiliation(s)
- G J Pryde
- Centre for Quantum Computer Technology, Department of Physics, University of Queensland, Brisbane 4072, Australia
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31
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O'Brien JL, Pryde GJ, White AG, Ralph TC, Branning D. Demonstration of an all-optical quantum controlled-NOT gate. Nature 2003; 426:264-7. [PMID: 14628045 DOI: 10.1038/nature02054] [Citation(s) in RCA: 183] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2003] [Accepted: 09/16/2003] [Indexed: 11/09/2022]
Abstract
The promise of tremendous computational power, coupled with the development of robust error-correcting schemes, has fuelled extensive efforts to build a quantum computer. The requirements for realizing such a device are confounding: scalable quantum bits (two-level quantum systems, or qubits) that can be well isolated from the environment, but also initialized, measured and made to undergo controllable interactions to implement a universal set of quantum logic gates. The usual set consists of single qubit rotations and a controlled-NOT (CNOT) gate, which flips the state of a target qubit conditional on the control qubit being in the state 1. Here we report an unambiguous experimental demonstration and comprehensive characterization of quantum CNOT operation in an optical system. We produce all four entangled Bell states as a function of only the input qubits' logical values, for a single operating condition of the gate. The gate is probabilistic (the qubits are destroyed upon failure), but with the addition of linear optical quantum non-demolition measurements, it is equivalent to the CNOT gate required for scalable all-optical quantum computation.
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Affiliation(s)
- J L O'Brien
- Centre for Quantum Computer Technology, Department of Physics, University of Queensland, Brisbane 4072, Australia.
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32
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Böttger T, Pryde GJ, Cone RL. Programmable laser frequency stabilization at 1523 nm by use of persistent spectral hole burning. Opt Lett 2003; 28:200-202. [PMID: 12656331 DOI: 10.1364/ol.28.000200] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Diode laser frequency stability of 2 kHz to 680 Hz over 20 ms to 500 s has been demonstrated at 1523 nm in the technologically important communication band by use of persistent spectral holes in the inhomogeneously broadened 4I15/2 --> 4I13/2 optical absorption of Er3+:D-:CaF2. Laser frequency stabilization was realized without vibrational or acoustical isolation of either the laser or spectral hole frequency reference, providing the means for implementing a versatile, compact, stable source.
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Affiliation(s)
- Thomas Böttger
- Department of Physics, The Spectrum Lab, Montana State University, Bozeman, Montana 59717, USA
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33
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Pryde GJ, Sellars MJ, Manson NB. Solid state coherent transient measurements using hard optical pulses. Phys Rev Lett 2000; 84:1152-1155. [PMID: 11017466 DOI: 10.1103/physrevlett.84.1152] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/23/1999] [Indexed: 05/23/2023]
Abstract
An isolated and spectrally narrow absorptive feature is prepared via a novel spectral hole burning process in an inhomogeneously broadened optical transition in Eu(3+):Y(2)SiO5. With the narrow feature it is shown that it is feasible to apply complex optical pulse sequences analogous to rf pulse sequences used extensively in NMR.
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Affiliation(s)
- GJ Pryde
- Laser Physics Centre, Research School of Physical Sciences and Engineering, The Australian National University, Canberra, ACT, 0200, Australia
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