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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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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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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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Sherman JA, Curtis MJ, Szwer DJ, Allcock DTC, Imreh G, Lucas DM, Steane AM. Experimental recovery of a qubit from partial collapse. Phys Rev Lett 2013; 111:180501. [PMID: 24237494 DOI: 10.1103/physrevlett.111.180501] [Citation(s) in RCA: 2] [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: 07/15/2013] [Indexed: 06/02/2023]
Abstract
We describe and implement a method to restore the state of a single qubit, in principle perfectly, after it has partially collapsed. The method resembles the classical Hahn spin echo but works on a wider class of relaxation processes, in which the quantum state partially leaves the computational Hilbert space. It is not guaranteed to work every time, but successful outcomes are heralded. We demonstrate, using a single trapped ion, a better performance from this recovery method than can be obtained employing projection and postselection alone. The demonstration features a novel qubit implementation that permits both partial collapse and coherent manipulations with high fidelity.
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Affiliation(s)
- J A Sherman
- Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom
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Abstract
Currently, laser cooling schemes are fundamentally based on the weak coupling regime. This requirement sets the trap frequency as an upper bound to the cooling rate. In this work we present a numerical study that shows the feasibility of cooling in the strong-coupling regime which then allows cooling rates that are faster than the trap frequency with experimentally feasible parameters. The scheme presented here can be applied to trapped atoms or ions as well as to mechanical oscillators. It can also cool medium sized ion chains close to the ground state.
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Affiliation(s)
- S Machnes
- Department of Physics and Astronomy, Tel-Aviv University, Tel Aviv 69978, Israel
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Myerson AH, Szwer DJ, Webster SC, Allcock DTC, Curtis MJ, Imreh G, Sherman JA, Stacey DN, Steane AM, Lucas DM. High-fidelity readout of trapped-ion qubits. Phys Rev Lett 2008; 100:200502. [PMID: 18518518 DOI: 10.1103/physrevlett.100.200502] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/12/2008] [Indexed: 05/26/2023]
Abstract
We demonstrate single-shot qubit readout with a fidelity sufficient for fault-tolerant quantum computation. For an optical qubit stored in 40Ca+ we achieve 99.991(1)% average readout fidelity in 10(6) trials, using time-resolved photon counting. An adaptive measurement technique allows 99.99% fidelity to be reached in 145 micros average detection time. For 43Ca+, we propose and implement an optical pumping scheme to transfer a long-lived hyperfine qubit to the optical qubit, capable of a theoretical fidelity of 99.95% in 10 micros. We achieve 99.87(4)% transfer fidelity and 99.77(3)% net readout fidelity.
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Affiliation(s)
- A H Myerson
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
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McDonnell MJ, Home JP, Lucas DM, Imreh G, Keitch BC, Szwer DJ, Thomas NR, Webster SC, Stacey DN, Steane AM. Long-lived mesoscopic entanglement outside the Lamb-Dicke regime. Phys Rev Lett 2007; 98:063603. [PMID: 17358940 DOI: 10.1103/physrevlett.98.063603] [Citation(s) in RCA: 6] [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: 05/15/2006] [Indexed: 05/14/2023]
Abstract
We create entangled states of the spin and motion of a single 40Ca+ ion in a linear ion trap. We theoretically study and experimentally observe the behavior outside the Lamb-Dicke regime, where the trajectory in phase space is modified and the motional coherent states become squeezed. We directly observe the modification of the return time of the trajectory, and infer the squeezing. The mesoscopic entanglement is observed up to Deltaalpha=5.1 with coherence time 170 micros and mean phonon excitation n = 16.
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Affiliation(s)
- M J McDonnell
- Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom
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McDonnell MJ, Stacey JP, Webster SC, Home JP, Ramos A, Lucas DM, Stacey DN, Steane AM. High-efficiency detection of a single quantum of angular momentum by suppression of optical pumping. Phys Rev Lett 2004; 93:153601. [PMID: 15524877 DOI: 10.1103/physrevlett.93.153601] [Citation(s) in RCA: 4] [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: 11/18/2003] [Indexed: 05/24/2023]
Abstract
We propose and demonstrate experimentally the discrimination between two spin states of an atom purely on the basis of their angular momentum. The discrimination relies on angular momentum selection rules and does not require magnetic effects such as a magnetic dipole moment of the atom or an applied magnetic field. The central ingredient is to prevent by coherent population trapping an optical pumping process which would otherwise relax the spin state before a detectable signal could be obtained. We detected the presence or absence of a single quantum (h) of angular momentum in a trapped calcium ion in a single observation with success probability 0.86. As a practical technique, the method can be applied to read out some types of quantum computer.
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Affiliation(s)
- M J McDonnell
- Centre for Quantum Computation, Department of Atomic and Laser Physics, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, England
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Lucas DM, Donald CJS, Home JP, McDonnell MJ, Ramos A, Stacey DN, Stacey JP, Steane AM, Webster SC. Oxford ion-trap quantum computing project. Philos Trans A Math Phys Eng Sci 2003; 361:1401-1408. [PMID: 12869316 DOI: 10.1098/rsta.2003.1209] [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
We describe recent progress in the development of an ion-trap quantum information processor. We discuss the choice of ion species and describe recent experiments on read-out for a ground-state qubit and photoionization trap loading.
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Affiliation(s)
- D M Lucas
- Centre for Quantum Computation, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, UK
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Arndt M, Szriftgiser P, Dalibard J, Steane AM. Atom optics in the time domain. Phys Rev A 1996; 53:3369-3378. [PMID: 9913281 DOI: 10.1103/physreva.53.3369] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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Townsend CG, Edwards NH, Cooper CJ, Zetie KP, Foot CJ, Steane AM, Szriftgiser P, Perrin H, Dalibard J. Phase-space density in the magneto-optical trap. Phys Rev A 1995; 52:1423-1440. [PMID: 9912381 DOI: 10.1103/physreva.52.1423] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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Aminoff CG, Steane AM, Bouyer P, Desbiolles P, Dalibard J, Cohen-Tannoudji C. Cesium atoms bouncing in a stable gravitational cavity. Phys Rev Lett 1993; 71:3083-3086. [PMID: 10054853 DOI: 10.1103/physrevlett.71.3083] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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