1
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Hendrickx NW, Massai L, Mergenthaler M, Schupp FJ, Paredes S, Bedell SW, Salis G, Fuhrer A. Sweet-spot operation of a germanium hole spin qubit with highly anisotropic noise sensitivity. Nat Mater 2024:10.1038/s41563-024-01857-5. [PMID: 38760518 DOI: 10.1038/s41563-024-01857-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/22/2023] [Accepted: 03/11/2024] [Indexed: 05/19/2024]
Abstract
Spin qubits defined by valence band hole states are attractive for quantum information processing due to their inherent coupling to electric fields, enabling fast and scalable qubit control. Heavy holes in germanium are particularly promising, with recent demonstrations of fast and high-fidelity qubit operations. However, the mechanisms and anisotropies that underlie qubit driving and decoherence remain mostly unclear. Here we report the highly anisotropic heavy-hole g-tensor and its dependence on electric fields, revealing how qubit driving and decoherence originate from electric modulations of the g-tensor. Furthermore, we confirm the predicted Ising-type hyperfine interaction and show that qubit coherence is ultimately limited by 1/f charge noise, where f is the frequency. Finally, operating the qubit at low magnetic field, we measure a dephasing time ofT 2 * = 17.6 μs, maintaining single-qubit gate fidelities well above 99% even at elevated temperatures of T > 1 K. This understanding of qubit driving and decoherence mechanisms is key towards realizing scalable and highly coherent hole qubit arrays.
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Affiliation(s)
- N W Hendrickx
- IBM Research Europe - Zurich, Rüschlikon, Switzerland.
| | - L Massai
- IBM Research Europe - Zurich, Rüschlikon, Switzerland
| | | | - F J Schupp
- IBM Research Europe - Zurich, Rüschlikon, Switzerland
| | - S Paredes
- IBM Research Europe - Zurich, Rüschlikon, Switzerland
| | - S W Bedell
- IBM Quantum, T.J. Watson Research Center, Yorktown Heights, NY, USA
| | - G Salis
- IBM Research Europe - Zurich, Rüschlikon, Switzerland
| | - A Fuhrer
- IBM Research Europe - Zurich, Rüschlikon, Switzerland.
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2
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John V, Borsoi F, György Z, Wang CA, Széchenyi G, van Riggelen-Doelman F, Lawrie WIL, Hendrickx NW, Sammak A, Scappucci G, Pályi A, Veldhorst M. Bichromatic Rabi Control of Semiconductor Qubits. Phys Rev Lett 2024; 132:067001. [PMID: 38394602 DOI: 10.1103/physrevlett.132.067001] [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: 08/04/2023] [Accepted: 10/20/2023] [Indexed: 02/25/2024]
Abstract
Electrically driven spin resonance is a powerful technique for controlling semiconductor spin qubits. However, it faces challenges in qubit addressability and off-resonance driving in larger systems. We demonstrate coherent bichromatic Rabi control of quantum dot hole spin qubits, offering a spatially selective approach for large qubit arrays. By applying simultaneous microwave bursts to different gate electrodes, we observe multichromatic resonance lines and resonance anticrossings that are caused by the ac Stark shift. Our theoretical framework aligns with experimental data, highlighting interdot motion as the dominant mechanism for bichromatic driving.
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Affiliation(s)
- Valentin John
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, P.O. Box 5046, 2600 GA Delft, Netherlands
| | - Francesco Borsoi
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, P.O. Box 5046, 2600 GA Delft, Netherlands
| | - Zoltán György
- ELTE Eötvös Loránd University, Institute of Physics, H-1117 Budapest, Hungary
| | - Chien-An Wang
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, P.O. Box 5046, 2600 GA Delft, Netherlands
| | - Gábor Széchenyi
- ELTE Eötvös Loránd University, Institute of Physics, H-1117 Budapest, Hungary
| | - Floor van Riggelen-Doelman
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, P.O. Box 5046, 2600 GA Delft, Netherlands
| | - William I L Lawrie
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, P.O. Box 5046, 2600 GA Delft, Netherlands
| | - Nico W Hendrickx
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, P.O. Box 5046, 2600 GA Delft, Netherlands
| | - Amir Sammak
- QuTech and Netherlands Organisation for Applied Scientific Research (TNO), Stieltjesweg 1, 2628 CK Delft, Netherlands
| | - Giordano Scappucci
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, P.O. Box 5046, 2600 GA Delft, Netherlands
| | - András Pályi
- Department of Theoretical Physics, Institute of Physics, Budapest University of Technology and Economics, Műegyetem rakpart 3, H-1111 Budapest, Hungary
- MTA-BME Quantum Dynamics and Correlations Research Group, Budapest University of Technology and Economics, Műegyetem rakpart 3, H-1111 Budapest, Hungary
| | - Menno Veldhorst
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, P.O. Box 5046, 2600 GA Delft, Netherlands
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3
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Borsoi F, Hendrickx NW, John V, Meyer M, Motz S, van Riggelen F, Sammak A, de Snoo SL, Scappucci G, Veldhorst M. Shared control of a 16 semiconductor quantum dot crossbar array. Nat Nanotechnol 2024; 19:21-27. [PMID: 37640909 PMCID: PMC10796274 DOI: 10.1038/s41565-023-01491-3] [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] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/10/2022] [Accepted: 07/20/2023] [Indexed: 08/31/2023]
Abstract
The efficient control of a large number of qubits is one of the most challenging aspects for practical quantum computing. Current approaches in solid-state quantum technology are based on brute-force methods, where each and every qubit requires at least one unique control line-an approach that will become unsustainable when scaling to the required millions of qubits. Here, inspired by random-access architectures in classical electronics, we introduce the shared control of semiconductor quantum dots to efficiently operate a two-dimensional crossbar array in planar germanium. We tune the entire array, comprising 16 quantum dots, to the few-hole regime. We then confine an odd number of holes in each site to isolate an unpaired spin per dot. Moving forward, we demonstrate on a vertical and a horizontal double quantum dot a method for the selective control of the interdot coupling and achieve a tunnel coupling tunability over more than 10 GHz. The operation of a quantum electronic device with fewer control terminals than tunable experimental parameters represents a compelling step forward in the construction of scalable quantum technology.
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Affiliation(s)
- Francesco Borsoi
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands.
| | - Nico W Hendrickx
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands
| | - Valentin John
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands
| | - Marcel Meyer
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands
| | - Sayr Motz
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands
| | - Floor van Riggelen
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands
| | - Amir Sammak
- QuTech and Netherlands Organisation for Applied Scientific Research (TNO), Delft, The Netherlands
| | - Sander L de Snoo
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands
| | - Giordano Scappucci
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands
| | - Menno Veldhorst
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands.
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4
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Lawrie WIL, Rimbach-Russ M, Riggelen FV, Hendrickx NW, Snoo SLD, Sammak A, Scappucci G, Helsen J, Veldhorst M. Simultaneous single-qubit driving of semiconductor spin qubits at the fault-tolerant threshold. Nat Commun 2023; 14:3617. [PMID: 37336892 DOI: 10.1038/s41467-023-39334-3] [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] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2021] [Accepted: 06/06/2023] [Indexed: 06/21/2023] Open
Abstract
Practical Quantum computing hinges on the ability to control large numbers of qubits with high fidelity. Quantum dots define a promising platform due to their compatibility with semiconductor manufacturing. Moreover, high-fidelity operations above 99.9% have been realized with individual qubits, though their performance has been limited to 98.67% when driving two qubits simultaneously. Here we present single-qubit randomized benchmarking in a two-dimensional array of spin qubits, finding native gate fidelities as high as 99.992(1)%. Furthermore, we benchmark single qubit gate performance while simultaneously driving two and four qubits, utilizing a novel benchmarking technique called N-copy randomized benchmarking, designed for simple experimental implementation and accurate simultaneous gate fidelity estimation. We find two- and four-copy randomized benchmarking fidelities of 99.905(8)% and 99.34(4)% respectively, and that next-nearest neighbor pairs are highly robust to cross-talk errors. These characterizations of single-qubit gate quality are crucial for scaling up quantum information technology.
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Affiliation(s)
- W I L Lawrie
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, Delft, the Netherlands
| | - M Rimbach-Russ
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, Delft, the Netherlands
| | - F van Riggelen
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, Delft, the Netherlands
| | - N W Hendrickx
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, Delft, the Netherlands
| | - S L de Snoo
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, Delft, the Netherlands
| | - A Sammak
- QuTech and Netherlands Organisation for Applied Scientific Research (TNO), Delft, the Netherlands
| | - G Scappucci
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, Delft, the Netherlands
| | - J Helsen
- QuSoft and CWI, Amsterdam, the Netherlands
| | - M Veldhorst
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, Delft, the Netherlands.
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5
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Meyer M, Déprez C, van Abswoude TR, Meijer IN, Liu D, Wang CA, Karwal S, Oosterhout S, Borsoi F, Sammak A, Hendrickx NW, Scappucci G, Veldhorst M. Electrical Control of Uniformity in Quantum Dot Devices. Nano Lett 2023; 23:2522-2529. [PMID: 36975126 PMCID: PMC10103318 DOI: 10.1021/acs.nanolett.2c04446] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/11/2022] [Revised: 03/20/2023] [Indexed: 06/18/2023]
Abstract
Highly uniform quantum systems are essential for the practical implementation of scalable quantum processors. While quantum dot spin qubits based on semiconductor technology are a promising platform for large-scale quantum computing, their small size makes them particularly sensitive to their local environment. Here, we present a method to electrically obtain a high degree of uniformity in the intrinsic potential landscape using hysteretic shifts of the gate voltage characteristics. We demonstrate the tuning of pinch-off voltages in quantum dot devices over hundreds of millivolts that then remain stable at least for hours. Applying our method, we homogenize the pinch-off voltages of the plunger gates in a linear array for four quantum dots, reducing the spread in pinch-off voltages by one order of magnitude. This work provides a new tool for the tuning of quantum dot devices and offers new perspectives for the implementation of scalable spin qubit arrays.
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Affiliation(s)
- Marcel Meyer
- QuTech
and Kavli Institute of Nanoscience, Delft
University of Technology, PO Box 5046, 2600 GA Delft, The Netherlands
| | - Corentin Déprez
- QuTech
and Kavli Institute of Nanoscience, Delft
University of Technology, PO Box 5046, 2600 GA Delft, The Netherlands
| | - Timo R. van Abswoude
- QuTech
and Kavli Institute of Nanoscience, Delft
University of Technology, PO Box 5046, 2600 GA Delft, The Netherlands
| | - Ilja N. Meijer
- QuTech
and Kavli Institute of Nanoscience, Delft
University of Technology, PO Box 5046, 2600 GA Delft, The Netherlands
| | - Dingshan Liu
- QuTech
and Kavli Institute of Nanoscience, Delft
University of Technology, PO Box 5046, 2600 GA Delft, The Netherlands
| | - Chien-An Wang
- QuTech
and Kavli Institute of Nanoscience, Delft
University of Technology, PO Box 5046, 2600 GA Delft, The Netherlands
| | - Saurabh Karwal
- QuTech
and Netherlands Organisation for Applied Scientific Research (TNO), PO Box 155, 2600 AD Delft, The Netherlands
| | - Stefan Oosterhout
- QuTech
and Netherlands Organisation for Applied Scientific Research (TNO), PO Box 155, 2600 AD Delft, The Netherlands
| | - Francesco Borsoi
- QuTech
and Kavli Institute of Nanoscience, Delft
University of Technology, PO Box 5046, 2600 GA Delft, The Netherlands
| | - Amir Sammak
- QuTech
and Netherlands Organisation for Applied Scientific Research (TNO), PO Box 155, 2600 AD Delft, The Netherlands
| | - Nico W. Hendrickx
- QuTech
and Kavli Institute of Nanoscience, Delft
University of Technology, PO Box 5046, 2600 GA Delft, The Netherlands
| | - Giordano Scappucci
- QuTech
and Kavli Institute of Nanoscience, Delft
University of Technology, PO Box 5046, 2600 GA Delft, The Netherlands
| | - Menno Veldhorst
- QuTech
and Kavli Institute of Nanoscience, Delft
University of Technology, PO Box 5046, 2600 GA Delft, The Netherlands
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6
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Corley-Wiciak C, Richter C, Zoellner MH, Zaitsev I, Manganelli CL, Zatterin E, Schülli TU, Corley-Wiciak AA, Katzer J, Reichmann F, Klesse WM, Hendrickx NW, Sammak A, Veldhorst M, Scappucci G, Virgilio M, Capellini G. Nanoscale Mapping of the 3D Strain Tensor in a Germanium Quantum Well Hosting a Functional Spin Qubit Device. ACS Appl Mater Interfaces 2023; 15:3119-3130. [PMID: 36598897 PMCID: PMC9869329 DOI: 10.1021/acsami.2c17395] [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] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/26/2022] [Accepted: 12/07/2022] [Indexed: 06/17/2023]
Abstract
A strained Ge quantum well, grown on a SiGe/Si virtual substrate and hosting two electrostatically defined hole spin qubits, is nondestructively investigated by synchrotron-based scanning X-ray diffraction microscopy to determine all its Bravais lattice parameters. This allows rendering the three-dimensional spatial dependence of the six strain tensor components with a lateral resolution of approximately 50 nm. Two different spatial scales governing the strain field fluctuations in proximity of the qubits are observed at <100 nm and >1 μm, respectively. The short-ranged fluctuations have a typical bandwidth of 2 × 10-4 and can be quantitatively linked to the compressive stressing action of the metal electrodes defining the qubits. By finite element mechanical simulations, it is estimated that this strain fluctuation is increased up to 6 × 10-4 at cryogenic temperature. The longer-ranged fluctuations are of the 10-3 order and are associated with misfit dislocations in the plastically relaxed virtual substrate. From this, energy variations of the light and heavy-hole energy maxima of the order of several 100 μeV and 1 meV are calculated for electrodes and dislocations, respectively. These insights over material-related inhomogeneities may feed into further modeling for optimization and design of large-scale quantum processors manufactured using the mainstream Si-based microelectronics technology.
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Affiliation(s)
- Cedric Corley-Wiciak
- IHP,
Leibniz-Institut für Innovative Mikroelektronik, Im Technologiepark 25, D-15236Frankfurt (Oder), Germany
| | - Carsten Richter
- IKZ,
Leibniz-Institut für Kristallzüchtung, Max-Born-Straße 2, D-12489Berlin, Germany
| | - Marvin H. Zoellner
- IHP,
Leibniz-Institut für Innovative Mikroelektronik, Im Technologiepark 25, D-15236Frankfurt (Oder), Germany
| | - Ignatii Zaitsev
- IHP,
Leibniz-Institut für Innovative Mikroelektronik, Im Technologiepark 25, D-15236Frankfurt (Oder), Germany
| | - Costanza L. Manganelli
- IHP,
Leibniz-Institut für Innovative Mikroelektronik, Im Technologiepark 25, D-15236Frankfurt (Oder), Germany
| | - Edoardo Zatterin
- ESRF,
European Synchrotron Radiation Facility, 71, Avenue des Martyrs, CS 40220, 38043Grenoble Cedex 9, France
| | - Tobias U. Schülli
- ESRF,
European Synchrotron Radiation Facility, 71, Avenue des Martyrs, CS 40220, 38043Grenoble Cedex 9, France
| | - Agnieszka A. Corley-Wiciak
- IHP,
Leibniz-Institut für Innovative Mikroelektronik, Im Technologiepark 25, D-15236Frankfurt (Oder), Germany
| | - Jens Katzer
- IHP,
Leibniz-Institut für Innovative Mikroelektronik, Im Technologiepark 25, D-15236Frankfurt (Oder), Germany
| | - Felix Reichmann
- IHP,
Leibniz-Institut für Innovative Mikroelektronik, Im Technologiepark 25, D-15236Frankfurt (Oder), Germany
| | - Wolfgang M. Klesse
- IHP,
Leibniz-Institut für Innovative Mikroelektronik, Im Technologiepark 25, D-15236Frankfurt (Oder), Germany
| | - Nico W. Hendrickx
- QuTech
and Kavli Institute of Nanoscience, Delft
University of Technology, Lorentzweg 1, 2628
CJDelft, The Netherlands
| | - Amir Sammak
- QuTech
and Netherlands Organisation for Applied Scientific Research (TNO), Stieltjesweg 1, 2628 CKDelft, The Netherlands
| | - Menno Veldhorst
- QuTech
and Kavli Institute of Nanoscience, Delft
University of Technology, Lorentzweg 1, 2628
CJDelft, The Netherlands
| | - Giordano Scappucci
- QuTech
and Kavli Institute of Nanoscience, Delft
University of Technology, Lorentzweg 1, 2628
CJDelft, The Netherlands
| | - Michele Virgilio
- Department
of Physics Enrico Fermi, Università
di Pisa, Pisa56126, Italy
| | - Giovanni Capellini
- IHP,
Leibniz-Institut für Innovative Mikroelektronik, Im Technologiepark 25, D-15236Frankfurt (Oder), Germany
- Dipartimento
di Scienze, Universita Roma Tre, Roma00146, Italy
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7
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Hendrickx NW, Fuhrer A. A spin qubit hiding from the noise. Nat Nanotechnol 2022; 17:1040-1041. [PMID: 36138205 DOI: 10.1038/s41565-022-01201-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
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8
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9
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Abstract
Qubits based on quantum dots have excellent prospects for scalable quantum technology due to their compatibility with standard semiconductor manufacturing. While early research focused on the simpler electron system, recent demonstrations using multi-hole quantum dots illustrated the favourable properties holes can offer for fast and scalable quantum control. Here, we establish a single-hole spin qubit in germanium and demonstrate the integration of single-shot readout and quantum control. We deplete a planar germanium double quantum dot to the last hole, confirmed by radio-frequency reflectrometry charge sensing. To demonstrate the integration of single-shot readout and qubit operation, we show Rabi driving on both qubits. We find remarkable electric control over the qubit resonance frequencies, providing great qubit addressability. Finally, we analyse the spin relaxation time, which we find to exceed one millisecond, setting the benchmark for hole quantum dot qubits. The ability to coherently manipulate a single hole spin underpins the quality of strained germanium and defines an excellent starting point for the construction of quantum hardware. While most results so far in semiconductor spin-based quantum computation use electron spins, devices based on hole spins may have more favourable properties for quantum applications. Here, the authors demonstrate single-shot readout and coherent control of a qubit made from a single hole spin.
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Affiliation(s)
- N W Hendrickx
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, P. O. Box 5046, 2600 GA, Delft, The Netherlands.
| | - W I L Lawrie
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, P. O. Box 5046, 2600 GA, Delft, The Netherlands
| | - L Petit
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, P. O. Box 5046, 2600 GA, Delft, The Netherlands
| | - A Sammak
- QuTech and Netherlands Organisation for Applied Scientific Research (TNO), Stieltjesweg 1, 2628 CK, Delft, The Netherlands
| | - G Scappucci
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, P. O. Box 5046, 2600 GA, Delft, The Netherlands
| | - M Veldhorst
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, P. O. Box 5046, 2600 GA, Delft, The Netherlands.
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10
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Hendrickx NW, Franke DP, Sammak A, Kouwenhoven M, Sabbagh D, Yeoh L, Li R, Tagliaferri MLV, Virgilio M, Capellini G, Scappucci G, Veldhorst M. Gate-controlled quantum dots and superconductivity in planar germanium. Nat Commun 2018; 9:2835. [PMID: 30026466 PMCID: PMC6053419 DOI: 10.1038/s41467-018-05299-x] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2018] [Accepted: 06/20/2018] [Indexed: 11/09/2022] Open
Abstract
Superconductors and semiconductors are crucial platforms in the field of quantum computing. They can be combined to hybrids, bringing together physical properties that enable the discovery of new emergent phenomena and provide novel strategies for quantum control. The involved semiconductor materials, however, suffer from disorder, hyperfine interactions or lack of planar technology. Here we realise an approach that overcomes these issues altogether and integrate gate-defined quantum dots and superconductivity into germanium heterostructures. In our system, heavy holes with mobilities exceeding 500,000 cm2 (Vs)-1 are confined in shallow quantum wells that are directly contacted by annealed aluminium leads. We observe proximity-induced superconductivity in the quantum well and demonstrate electric gate-control of the supercurrent. Germanium therefore has great promise for fast and coherent quantum hardware and, being compatible with standard manufacturing, could become a leading material for quantum information processing.
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Affiliation(s)
- N W Hendrickx
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, PO Box 5046, 2600 GA, Delft, The Netherlands.
| | - D P Franke
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, PO Box 5046, 2600 GA, Delft, The Netherlands
| | - A Sammak
- QuTech and the Netherlands Organisation for Applied Scientific Research (TNO), Stieltjesweg 1, 2628 CK, Delft, The Netherlands
| | - M Kouwenhoven
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, PO Box 5046, 2600 GA, Delft, The Netherlands
| | - D Sabbagh
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, PO Box 5046, 2600 GA, Delft, The Netherlands
| | - L Yeoh
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, PO Box 5046, 2600 GA, Delft, The Netherlands
| | - R Li
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, PO Box 5046, 2600 GA, Delft, The Netherlands
| | - M L V Tagliaferri
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, PO Box 5046, 2600 GA, Delft, The Netherlands
| | - M Virgilio
- Dipartimento di Fisica "E. Fermi", Università di Pisa, Largo Pontecorvo 3, 56127, Pisa, Italy
| | - G Capellini
- Dipartimento di Scienze, Università degli studi Roma Tre, Viale Marconi 446, 00146, Roma, Italy
- IHP, Im Technologiepark 25, 15236, Frankfurt (Oder), Germany
| | - G Scappucci
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, PO Box 5046, 2600 GA, Delft, The Netherlands
| | - M Veldhorst
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, PO Box 5046, 2600 GA, Delft, The Netherlands.
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