1
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Drmota P, Nadlinger DP, Main D, Nichol BC, Ainley EM, Leichtle D, Mantri A, Kashefi E, Srinivas R, Araneda G, Ballance CJ, Lucas DM. Verifiable Blind Quantum Computing with Trapped Ions and Single Photons. Phys Rev Lett 2024; 132:150604. [PMID: 38682960 DOI: 10.1103/physrevlett.132.150604] [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: 05/10/2023] [Accepted: 01/16/2024] [Indexed: 05/01/2024]
Abstract
We report the first hybrid matter-photon implementation of verifiable blind quantum computing. We use a trapped-ion quantum server and a client-side photonic detection system networked via a fiber-optic quantum link. The availability of memory qubits and deterministic entangling gates enables interactive protocols without postselection-key requirements for any scalable blind server, which previous realizations could not provide. We quantify the privacy at ≲0.03 leaked classical bits per qubit. This experiment demonstrates a path to fully verified quantum computing in the cloud.
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Affiliation(s)
- P Drmota
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - D P Nadlinger
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - D Main
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - B C Nichol
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - E M Ainley
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - D Leichtle
- Laboratoire d'Informatique de Paris 6, CNRS, Sorbonne Université, Paris 75005, France
| | - A Mantri
- Joint Center for Quantum Information and Computer Science, University of Maryland, College Park, Maryland, USA
| | - E Kashefi
- Laboratoire d'Informatique de Paris 6, CNRS, Sorbonne Université, Paris 75005, France
- School of Informatics, University of Edinburgh, Edinburgh EH8 9AB, United Kingdom
| | - R Srinivas
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - G Araneda
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - C J Ballance
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - D M Lucas
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
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2
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Saner S, Băzăvan O, Minder M, Drmota P, Webb DJ, Araneda G, Srinivas R, Lucas DM, Ballance CJ. Breaking the Entangling Gate Speed Limit for Trapped-Ion Qubits Using a Phase-Stable Standing Wave. Phys Rev Lett 2023; 131:220601. [PMID: 38101375 DOI: 10.1103/physrevlett.131.220601] [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: 05/31/2023] [Accepted: 10/16/2023] [Indexed: 12/17/2023]
Abstract
All laser-driven entangling operations for trapped-ion qubits have hitherto been performed without control of the optical phase of the light field, which precludes independent tuning of the carrier and motional coupling. By placing ^{88}Sr^{+} ions in a λ=674 nm standing wave, whose relative position is controlled to ≈λ/100, we suppress the carrier coupling by a factor of 18, while coherently enhancing the spin-motion coupling. We experimentally demonstrate that the off-resonant carrier coupling imposes a speed limit for conventional traveling-wave Mølmer-Sørensen gates; we use the standing wave to surpass this limit and achieve a gate duration of 15 μs, restricted by the available laser power.
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Affiliation(s)
- S Saner
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - O Băzăvan
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - M Minder
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - P Drmota
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - D J Webb
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - G Araneda
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - R Srinivas
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - D M Lucas
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - C J Ballance
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
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3
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Srinivas R, Löschnauer CM, Malinowski M, Hughes AC, Nourshargh R, Negnevitsky V, Allcock DTC, King SA, Matthiesen C, Harty TP, Ballance CJ. Coherent Control of Trapped-Ion Qubits with Localized Electric Fields. Phys Rev Lett 2023; 131:020601. [PMID: 37505962 DOI: 10.1103/physrevlett.131.020601] [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: 10/28/2022] [Accepted: 05/23/2023] [Indexed: 07/30/2023]
Abstract
We present a new method for coherent control of trapped ion qubits in separate interaction regions of a multizone trap by simultaneously applying an electric field and a spin-dependent gradient. Both the phase and amplitude of the effective single-qubit rotation depend on the electric field, which can be localized to each zone. We demonstrate this interaction on a single ion using both laser-based and magnetic-field gradients in a surface-electrode ion trap, and measure the localization of the electric field.
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Affiliation(s)
- R Srinivas
- Oxford Ionics, Oxford, OX5 1PF, United Kingdom
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford, OX1 3PU, United Kingdom
| | | | | | - A C Hughes
- Oxford Ionics, Oxford, OX5 1PF, United Kingdom
| | | | | | - D T C Allcock
- Oxford Ionics, Oxford, OX5 1PF, United Kingdom
- Department of Physics, University of Oregon, Eugene, Oregon 97403, USA
| | - S A King
- Oxford Ionics, Oxford, OX5 1PF, United Kingdom
| | | | - T P Harty
- Oxford Ionics, Oxford, OX5 1PF, United Kingdom
| | - C J Ballance
- Oxford Ionics, Oxford, OX5 1PF, United Kingdom
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford, OX1 3PU, United Kingdom
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4
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Drmota P, Main D, Nadlinger DP, Nichol BC, Weber MA, Ainley EM, Agrawal A, Srinivas R, Araneda G, Ballance CJ, Lucas DM. Robust Quantum Memory in a Trapped-Ion Quantum Network Node. Phys Rev Lett 2023; 130:090803. [PMID: 36930909 DOI: 10.1103/physrevlett.130.090803] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/27/2022] [Accepted: 01/19/2023] [Indexed: 06/18/2023]
Abstract
We integrate a long-lived memory qubit into a mixed-species trapped-ion quantum network node. Ion-photon entanglement first generated with a network qubit in ^{88}Sr^{+} is transferred to ^{43}Ca^{+} with 0.977(7) fidelity, and mapped to a robust memory qubit. We then entangle the network qubit with a second photon, without affecting the memory qubit. We perform quantum state tomography to show that the fidelity of ion-photon entanglement decays ∼70 times slower on the memory qubit. Dynamical decoupling further extends the storage duration; we measure an ion-photon entanglement fidelity of 0.81(4) after 10 s.
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Affiliation(s)
- P Drmota
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - D Main
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - D P Nadlinger
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - B C Nichol
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - M A Weber
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - E M Ainley
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - A Agrawal
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - R Srinivas
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - G Araneda
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - C J Ballance
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - D M Lucas
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
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5
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Nichol BC, Srinivas R, Nadlinger DP, Drmota P, Main D, Araneda G, Ballance CJ, Lucas DM. An elementary quantum network of entangled optical atomic clocks. Nature 2022; 609:689-694. [PMID: 36071166 DOI: 10.1038/s41586-022-05088-z] [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] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2021] [Accepted: 07/07/2022] [Indexed: 11/09/2022]
Abstract
Optical atomic clocks are our most precise tools to measure time and frequency1-3. Precision frequency comparisons between clocks in separate locations enable one to probe the space-time variation of fundamental constants4,5 and the properties of dark matter6,7, to perform geodesy8-10 and to evaluate systematic clock shifts. Measurements on independent systems are limited by the standard quantum limit; measurements on entangled systems can surpass the standard quantum limit to reach the ultimate precision allowed by quantum theory-the Heisenberg limit. Although local entangling operations have demonstrated this enhancement at microscopic distances11-16, comparisons between remote atomic clocks require the rapid generation of high-fidelity entanglement between systems that have no intrinsic interactions. Here we report the use of a photonic link17,18 to entangle two 88Sr+ ions separated by a macroscopic distance19 (approximately 2 m) to demonstrate an elementary quantum network of entangled optical clocks. For frequency comparisons between the ions, we find that entanglement reduces the measurement uncertainty by nearly [Formula: see text], the value predicted for the Heisenberg limit. Today's optical clocks are typically limited by dephasing of the probe laser20; in this regime, we find that entanglement yields a factor of 2 reduction in the measurement uncertainty compared with conventional correlation spectroscopy techniques20-22. We demonstrate this enhancement for the measurement of a frequency shift applied to one of the clocks. This two-node network could be extended to additional nodes23, to other species of trapped particles or-through local operations-to larger entangled systems.
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Affiliation(s)
- B C Nichol
- Department of Physics, Clarendon Laboratory, University of Oxford, Oxford, UK.
| | - R Srinivas
- Department of Physics, Clarendon Laboratory, University of Oxford, Oxford, UK.
| | - D P Nadlinger
- Department of Physics, Clarendon Laboratory, University of Oxford, Oxford, UK
| | - P Drmota
- Department of Physics, Clarendon Laboratory, University of Oxford, Oxford, UK
| | - D Main
- Department of Physics, Clarendon Laboratory, University of Oxford, Oxford, UK
| | - G Araneda
- Department of Physics, Clarendon Laboratory, University of Oxford, Oxford, UK
| | - C J Ballance
- Department of Physics, Clarendon Laboratory, University of Oxford, Oxford, UK
| | - D M Lucas
- Department of Physics, Clarendon Laboratory, University of Oxford, Oxford, UK
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6
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Nadlinger DP, Drmota P, Nichol BC, Araneda G, Main D, Srinivas R, Lucas DM, Ballance CJ, Ivanov K, Tan EYZ, Sekatski P, Urbanke RL, Renner R, Sangouard N, Bancal JD. Experimental quantum key distribution certified by Bell's theorem. Nature 2022; 607:682-686. [PMID: 35896644 DOI: 10.1038/s41586-022-04941-5] [Citation(s) in RCA: 17] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2021] [Accepted: 06/07/2022] [Indexed: 11/09/2022]
Abstract
Cryptographic key exchange protocols traditionally rely on computational conjectures such as the hardness of prime factorization1 to provide security against eavesdropping attacks. Remarkably, quantum key distribution protocols such as the Bennett-Brassard scheme2 provide information-theoretic security against such attacks, a much stronger form of security unreachable by classical means. However, quantum protocols realized so far are subject to a new class of attacks exploiting a mismatch between the quantum states or measurements implemented and their theoretical modelling, as demonstrated in numerous experiments3-6. Here we present the experimental realization of a complete quantum key distribution protocol immune to these vulnerabilities, following Ekert's pioneering proposal7 to use entanglement to bound an adversary's information from Bell's theorem8. By combining theoretical developments with an improved optical fibre link generating entanglement between two trapped-ion qubits, we obtain 95,628 key bits with device-independent security9-12 from 1.5 million Bell pairs created during eight hours of run time. We take steps to ensure that information on the measurement results is inaccessible to an eavesdropper. These measurements are performed without space-like separation. Our result shows that provably secure cryptography under general assumptions is possible with real-world devices, and paves the way for further quantum information applications based on the device-independence principle.
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Affiliation(s)
- D P Nadlinger
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, UK.
| | - P Drmota
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, UK
| | - B C Nichol
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, UK
| | - G Araneda
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, UK
| | - D Main
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, UK
| | - R Srinivas
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, UK
| | - D M Lucas
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, UK
| | - C J Ballance
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, UK.
| | - K Ivanov
- School of Computer and Communication Sciences, EPFL, Lausanne, Switzerland
| | - E Y-Z Tan
- Institute for Theoretical Physics, ETH Zürich, Zürich, Switzerland
| | - P Sekatski
- Department of Applied Physics, University of Geneva, Geneva, Switzerland
| | - R L Urbanke
- School of Computer and Communication Sciences, EPFL, Lausanne, Switzerland
| | - R Renner
- Institute for Theoretical Physics, ETH Zürich, Zürich, Switzerland
| | - N Sangouard
- Université Paris-Saclay, CEA, CNRS, Institut de Physique Théorique, Gif-sur-Yvette, France.
| | - J-D Bancal
- Université Paris-Saclay, CEA, CNRS, Institut de Physique Théorique, Gif-sur-Yvette, France.
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7
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Hughes AC, Schäfer VM, Thirumalai K, Nadlinger DP, Woodrow SR, Lucas DM, Ballance CJ. Benchmarking a High-Fidelity Mixed-Species Entangling Gate. Phys Rev Lett 2020; 125:080504. [PMID: 32909787 DOI: 10.1103/physrevlett.125.080504] [Citation(s) in RCA: 2] [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: 05/04/2020] [Accepted: 07/08/2020] [Indexed: 06/11/2023]
Abstract
We implement a two-qubit logic gate between a ^{43}Ca^{+} hyperfine qubit and a ^{88}Sr^{+} Zeeman qubit. For this pair of ion species, the S-P optical transitions are close enough that a single laser of wavelength 402 nm can be used to drive the gate but sufficiently well separated to give good spectral isolation and low photon scattering errors. We characterize the gate by full randomized benchmarking, gate set tomography, and Bell state analysis. The latter method gives a fidelity of 99.8(1)%, comparable to that of the best same-species gates and consistent with known sources of error.
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Affiliation(s)
- A C Hughes
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - V M Schäfer
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - K Thirumalai
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - D P Nadlinger
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - S R Woodrow
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - D M Lucas
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - C J Ballance
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
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8
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Stephenson LJ, Nadlinger DP, Nichol BC, An S, Drmota P, Ballance TG, Thirumalai K, Goodwin JF, Lucas DM, Ballance CJ. High-Rate, High-Fidelity Entanglement of Qubits Across an Elementary Quantum Network. Phys Rev Lett 2020; 124:110501. [PMID: 32242699 DOI: 10.1103/physrevlett.124.110501] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/03/2019] [Accepted: 02/06/2020] [Indexed: 06/11/2023]
Abstract
We demonstrate remote entanglement of trapped-ion qubits via a quantum-optical fiber link with fidelity and rate approaching those of local operations. Two ^{88}Sr^{+} qubits are entangled via the polarization degree of freedom of two spontaneously emitted 422 nm photons which are coupled by high-numerical-aperture lenses into single-mode optical fibers and interfere on a beam splitter. A novel geometry allows high-efficiency photon collection while maintaining unit fidelity for ion-photon entanglement. We generate heralded Bell pairs with fidelity 94% at an average rate 182 s^{-1} (success probability 2.18×10^{-4}).
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Affiliation(s)
- L J Stephenson
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - D P Nadlinger
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - B C Nichol
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - S An
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - P Drmota
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - T G Ballance
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - K Thirumalai
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - J F Goodwin
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - D M Lucas
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - C J Ballance
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
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9
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Sepiol MA, Hughes AC, Tarlton JE, Nadlinger DP, Ballance TG, Ballance CJ, Harty TP, Steane AM, Goodwin JF, Lucas DM. Probing Qubit Memory Errors at the Part-per-Million Level. Phys Rev Lett 2019; 123:110503. [PMID: 31573247 DOI: 10.1103/physrevlett.123.110503] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/10/2019] [Indexed: 06/10/2023]
Abstract
Robust qubit memory is essential for quantum computing, both for near-term devices operating without error correction, and for the long-term goal of a fault-tolerant processor. We directly measure the memory error ε_{m} for a ^{43}Ca^{+} trapped-ion qubit in the small-error regime and find ε_{m}<10^{-4} for storage times t≲50 ms. This exceeds gate or measurement times by three orders of magnitude. Using randomized benchmarking, at t=1 ms we measure ε_{m}=1.2(7)×10^{-6}, around ten times smaller than that extrapolated from the T_{2}^{*} time, and limited by instability of the atomic clock reference used to benchmark the qubit.
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Affiliation(s)
- M A Sepiol
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - A C Hughes
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - J E Tarlton
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - D P Nadlinger
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - T G Ballance
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - C J Ballance
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - T P Harty
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - A M Steane
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - J F Goodwin
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - D M Lucas
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
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10
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Merkel B, Thirumalai K, Tarlton JE, Schäfer VM, Ballance CJ, Harty TP, Lucas DM. Magnetic field stabilization system for atomic physics experiments. Rev Sci Instrum 2019; 90:044702. [PMID: 31042982 DOI: 10.1063/1.5080093] [Citation(s) in RCA: 4] [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: 11/05/2018] [Accepted: 03/25/2019] [Indexed: 06/09/2023]
Abstract
Atomic physics experiments commonly use millitesla-scale magnetic fields to provide a quantization axis. As atomic transition frequencies depend on the magnitude of this field, many experiments require a stable absolute field. Most setups use electromagnets, which require a power supply stability not usually met by commercially available units. We demonstrate the stabilization of a field of 14.6 mT to 4.3 nT rms noise (0.29 ppm), compared to noise of >100 nT without any stabilization. The rms noise is measured using a field-dependent hyperfine transition in a single 43Ca+ ion held in a Paul trap at the center of the magnetic field coils. For the 43Ca+ "atomic clock" qubit transition at 14.6 mT, which depends on the field only in second order, this would yield a projected coherence time of many hours. Our system consists of a feedback loop and a feedforward circuit that control the current through the field coils and could easily be adapted to other field amplitudes, making it suitable for other applications such as neutral atom traps.
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Affiliation(s)
- B Merkel
- Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom
| | - K Thirumalai
- Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom
| | - J E Tarlton
- Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom
| | - V M Schäfer
- Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom
| | - C J Ballance
- Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom
| | - T P Harty
- Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom
| | - D M Lucas
- Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom
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11
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Ballance TG, Goodwin JF, Nichol B, Stephenson LJ, Ballance CJ, Lucas DM. A short response time atomic source for trapped ion experiments. Rev Sci Instrum 2018; 89:053102. [PMID: 29864886 DOI: 10.1063/1.5025713] [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: 06/08/2023]
Abstract
Ion traps are often loaded from atomic beams produced by resistively heated ovens. We demonstrate an atomic oven which has been designed for fast control of the atomic flux density and reproducible construction. We study the limiting time constants of the system and, in tests with 40Ca, show that we can reach the desired level of flux in 12 s, with no overshoot. Our results indicate that it may be possible to achieve an even faster response by applying an appropriate one-off heat treatment to the oven before it is used.
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Affiliation(s)
- T G Ballance
- Clarendon Laboratory, Parks Rd., Oxford OX1 3PU, United Kingdom
| | - J F Goodwin
- Clarendon Laboratory, Parks Rd., Oxford OX1 3PU, United Kingdom
| | - B Nichol
- Clarendon Laboratory, Parks Rd., Oxford OX1 3PU, United Kingdom
| | - L J Stephenson
- Clarendon Laboratory, Parks Rd., Oxford OX1 3PU, United Kingdom
| | - C J Ballance
- Clarendon Laboratory, Parks Rd., Oxford OX1 3PU, United Kingdom
| | - D M Lucas
- Clarendon Laboratory, Parks Rd., Oxford OX1 3PU, United Kingdom
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12
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Schäfer VM, Ballance CJ, Thirumalai K, Stephenson LJ, Ballance TG, Steane AM, Lucas DM. Fast quantum logic gates with trapped-ion qubits. Nature 2018; 555:75-78. [DOI: 10.1038/nature25737] [Citation(s) in RCA: 139] [Impact Index Per Article: 23.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2017] [Accepted: 01/09/2018] [Indexed: 01/14/2023]
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13
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Harty TP, Sepiol MA, Allcock DTC, Ballance CJ, Tarlton JE, Lucas DM. High-Fidelity Trapped-Ion Quantum Logic Using Near-Field Microwaves. Phys Rev Lett 2016; 117:140501. [PMID: 27740823 DOI: 10.1103/physrevlett.117.140501] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2016] [Indexed: 06/06/2023]
Abstract
We demonstrate a two-qubit logic gate driven by near-field microwaves in a room-temperature microfabricated surface ion trap. We introduce a dynamically decoupled gate method, which stabilizes the qubits against fluctuating energy shifts and avoids the need to null the microwave field. We use the gate to produce a Bell state with fidelity 99.7(1)%, after accounting for state preparation and measurement errors. The gate is applied directly to ^{43}Ca^{+} hyperfine "atomic clock" qubits (coherence time T_{2}^{*}≈50 s) using the oscillating magnetic field gradient produced by an integrated microwave electrode.
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Affiliation(s)
- T P Harty
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - M A Sepiol
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - D T C Allcock
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - C J Ballance
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - J E Tarlton
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - D M Lucas
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
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Ballance CJ, Harty TP, Linke NM, Sepiol MA, Lucas DM. High-Fidelity Quantum Logic Gates Using Trapped-Ion Hyperfine Qubits. Phys Rev Lett 2016; 117:060504. [PMID: 27541450 DOI: 10.1103/physrevlett.117.060504] [Citation(s) in RCA: 117] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/30/2015] [Indexed: 05/02/2023]
Abstract
We demonstrate laser-driven two-qubit and single-qubit logic gates with respective fidelities 99.9(1)% and 99.9934(3)%, significantly above the ≈99% minimum threshold level required for fault-tolerant quantum computation, using qubits stored in hyperfine ground states of calcium-43 ions held in a room-temperature trap. We study the speed-fidelity trade-off for the two-qubit gate, for gate times between 3.8 μs and 520 μs, and develop a theoretical error model which is consistent with the data and which allows us to identify the principal technical sources of infidelity.
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Affiliation(s)
- C J Ballance
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - T P Harty
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - N M Linke
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - M A Sepiol
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - D M Lucas
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
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15
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Ballance CJ, Schäfer VM, Home JP, Szwer DJ, Webster SC, Allcock DTC, Linke NM, Harty TP, Aude Craik DPL, Stacey DN, Steane AM, Lucas DM. Hybrid quantum logic and a test of Bell's inequality using two different atomic isotopes. Nature 2016; 528:384-6. [PMID: 26672554 DOI: 10.1038/nature16184] [Citation(s) in RCA: 71] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2015] [Accepted: 10/26/2015] [Indexed: 11/09/2022]
Abstract
Entanglement is one of the most fundamental properties of quantum mechanics, and is the key resource for quantum information processing (QIP). Bipartite entangled states of identical particles have been generated and studied in several experiments, and post-selected or heralded entangled states involving pairs of photons, single photons and single atoms, or different nuclei in the solid state, have also been produced. Here we use a deterministic quantum logic gate to generate a 'hybrid' entangled state of two trapped-ion qubits held in different isotopes of calcium, perform full tomography of the state produced, and make a test of Bell's inequality with non-identical atoms. We use a laser-driven two-qubit gate, whose mechanism is insensitive to the qubits' energy splittings, to produce a maximally entangled state of one (40)Ca(+) qubit and one (43)Ca(+) qubit, held 3.5 micrometres apart in the same ion trap, with 99.8 ± 0.6 per cent fidelity. We test the CHSH (Clauser-Horne-Shimony-Holt) version of Bell's inequality for this novel entangled state and find that it is violated by 15 standard deviations; in this test, we close the detection loophole but not the locality loophole. Mixed-species quantum logic is a powerful technique for the construction of a quantum computer based on trapped ions, as it allows protection of memory qubits while other qubits undergo logic operations or are used as photonic interfaces to other processing units. The entangling gate mechanism used here can also be applied to qubits stored in different atomic elements; this would allow both memory and logic gate errors caused by photon scattering to be reduced below the levels required for fault-tolerant quantum error correction, which is an essential prerequisite for general-purpose quantum computing.
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Affiliation(s)
- C J Ballance
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, UK
| | - V M Schäfer
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, UK
| | - J P Home
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, UK
| | - D J Szwer
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, UK
| | - S C Webster
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, UK
| | - D T C Allcock
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, UK
| | - N M Linke
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, UK
| | - T P Harty
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, UK
| | - D P L Aude Craik
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, UK
| | - D N Stacey
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, UK
| | - A M Steane
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, UK
| | - D M Lucas
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, UK
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16
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Schäfer VM, Ballance CJ, Tock CJ, Lucas DM. Optical injection and spectral filtering of high-power ultraviolet laser diodes. Opt Lett 2015; 40:4265-4268. [PMID: 26371912 DOI: 10.1364/ol.40.004265] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We demonstrate injection locking of high-power laser diodes operating at 397 nm. We achieve stable operation with an injection power of ∼100 μW and a slave laser output power of up to 110 mW. We investigate the spectral purity of the slave laser light via photon scattering experiments on a single trapped (40)Ca(+) ion. We show that it is possible to achieve a scattering rate indistinguishable from that of monochromatic light by filtering the laser light with a diffraction grating to remove amplified spontaneous emission.
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17
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Harty TP, Allcock DTC, Ballance CJ, Guidoni L, Janacek HA, Linke NM, Stacey DN, Lucas DM. High-Fidelity Preparation, Gates, Memory, and Readout of a Trapped-Ion Quantum Bit. Phys Rev Lett 2014; 113:220501. [PMID: 25494060 DOI: 10.1103/physrevlett.113.220501] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/19/2014] [Indexed: 06/04/2023]
Abstract
We implement all single-qubit operations with fidelities significantly above the minimum threshold required for fault-tolerant quantum computing, using a trapped-ion qubit stored in hyperfine "atomic clock" states of ^{43}Ca^{+}. We measure a combined qubit state preparation and single-shot readout fidelity of 99.93%, a memory coherence time of T_{2}^{*}=50 sec, and an average single-qubit gate fidelity of 99.9999%. These results are achieved in a room-temperature microfabricated surface trap, without the use of magnetic field shielding or dynamic decoupling techniques to overcome technical noise.
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Affiliation(s)
- T P Harty
- Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom
| | - D T C Allcock
- Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom
| | - C J Ballance
- Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom
| | - L Guidoni
- Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom and Laboratoire Matériaux et Phénomènes Quantiques, University of Paris Diderot, UMR 7162 CNRS, F-75205 Paris, France
| | - H A Janacek
- Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom
| | - N M Linke
- Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom
| | - D N Stacey
- Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom
| | - D M Lucas
- Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom
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18
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Linke NM, Ballance CJ, Lucas DM. Injection locking of two frequency-doubled lasers with 3.2 GHz offset for driving Raman transitions with low photon scattering in 43Ca+. Opt Lett 2013; 38:5087-5089. [PMID: 24281516 DOI: 10.1364/ol.38.005087] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
We describe the injection locking of two infrared (794 nm) laser diodes that are each part of a frequency-doubled laser system. An acousto-optic modulator in the injection path gives an offset of 1.6 GHz between the lasers for driving Raman transitions between states in the hyperfine split (by 3.2 GHz) ground level of 43Ca+. The offset can be disabled for use in 40Ca+. We measure the relative linewidth of the frequency-doubled beams to be 42 mHz in an optical heterodyne measurement. The use of both injection locking and frequency doubling combines spectral purity with high optical power. Our scheme is applicable for providing Raman beams across other ion species and neutral atoms where coherent optical manipulation is required.
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