Publication Date:
2014-07-22
Description:
Quantum error correction is required for a practical quantum computer because of the fragile nature of quantum information. In quantum error correction, information is redundantly stored in a large quantum state space and one or more observables must be monitored to reveal the occurrence of an error, without disturbing the information encoded in an unknown quantum state. Such observables, typically multi-quantum-bit parities, must correspond to a special symmetry property inherent in the encoding scheme. Measurements of these observables, or error syndromes, must also be performed in a quantum non-demolition way (projecting without further perturbing the state) and more quickly than errors occur. Previously, quantum non-demolition measurements of quantum jumps between states of well-defined energy have been performed in systems such as trapped ions, electrons, cavity quantum electrodynamics, nitrogen-vacancy centres and superconducting quantum bits. So far, however, no fast and repeated monitoring of an error syndrome has been achieved. Here we track the quantum jumps of a possible error syndrome, namely the photon number parity of a microwave cavity, by mapping this property onto an ancilla quantum bit, whose only role is to facilitate quantum state manipulation and measurement. This quantity is just the error syndrome required in a recently proposed scheme for a hardware-efficient protected quantum memory using Schrodinger cat states (quantum superpositions of different coherent states of light) in a harmonic oscillator. We demonstrate the projective nature of this measurement onto a region of state space with well-defined parity by observing the collapse of a coherent state onto even or odd cat states. The measurement is fast compared with the cavity lifetime, has a high single-shot fidelity and has a 99.8 per cent probability per single measurement of leaving the parity unchanged. In combination with the deterministic encoding of quantum information in cat states realized earlier, the quantum non-demolition parity tracking that we demonstrate represents an important step towards implementing an active system that extends the lifetime of a quantum bit.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Sun, L -- Petrenko, A -- Leghtas, Z -- Vlastakis, B -- Kirchmair, G -- Sliwa, K M -- Narla, A -- Hatridge, M -- Shankar, S -- Blumoff, J -- Frunzio, L -- Mirrahimi, M -- Devoret, M H -- Schoelkopf, R J -- England -- Nature. 2014 Jul 24;511(7510):444-8. doi: 10.1038/nature13436. Epub 2014 Jul 13.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉1] Departments of Applied Physics and Physics, Yale University, New Haven, Connecticut 06511, USA [2] Center for Quantum Information, Institute for Interdisciplinary Information Sciences, Tsinghua University, Beijing 100084, China (L.S.); Institut fur Experimentalphysik, Universitat Innsbruck, Technikerstrasse 25, A-6020 Innsbruck, Austria and Institut fur Quantenoptik und Quanteninformation, Osterreichische Akademie der Wissenschaften, Otto-Hittmair-Platz 1, A-6020 Innsbruck, Austria (G.K.). ; Departments of Applied Physics and Physics, Yale University, New Haven, Connecticut 06511, USA. ; 1] Departments of Applied Physics and Physics, Yale University, New Haven, Connecticut 06511, USA [2] INRIA Paris-Rocquencourt, Domaine de Voluceau, BP 105, 78153 Le Chesnay Cedex, France.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25043007" target="_blank"〉PubMed〈/a〉
Print ISSN:
0028-0836
Electronic ISSN:
1476-4687
Topics:
Biology
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Chemistry and Pharmacology
,
Medicine
,
Natural Sciences in General
,
Physics
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