Journal
NATURE NANOTECHNOLOGY
Volume 14, Issue 6, Pages 555-+Publisher
NATURE PORTFOLIO
DOI: 10.1038/s41565-019-0426-x
Keywords
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Funding
- CREST, JST [JPMJCR15N2, JPMJCR1675]
- ImPACT Program of the Council for Science, Technology and Innovation (Cabinet Office, Government of Japan)
- JSPS KAKENHI [26220710, JP16H02204, 18H01819, 16H00817, 17H05187]
- RIKEN Incentive Research Projects
- Q-LEAP project
- PRESTO [JPMJPR16N3]
- JST
- Yazaki Memorial Foundation for Science and Technology Research Grant
- Advanced Technology Institute Research Grant
- Murata Science Foundation Research Grant
- Izumi Science and Technology Foundation Research Grant
- TEPCO Memorial Foundation Research Grant
- Thermal & Electric Energy Technology Foundation Research Grant
- Telecommunications Advancement Foundation Research Grant
- Futaba Electronics Memorial Foundation Research Grant
- MST Foundation Research Grant
- DFH/UFA [CDFA-05-06]
- MEXT, Japan
- BMBF - Q.Link.X [16KIS0867]
- [TRR160]
- Grants-in-Aid for Scientific Research [18H01819, 16H00817, 17H05187] Funding Source: KAKEN
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Measurements of quantum systems inevitably involve disturbance in various forms. Within the limits imposed by quantum mechanics, there exists an ideal projective measurement that does not introduce a back action on the measured observable, known as a quantum non-demolition (QND) measurement(1,2). Here we demonstrate an all-electrical QND measurement of a single electron spin in a gate-defined quantum dot. We entangle the single spin with a two-electron, singlet-triplet ancilla qubit via the exchange interaction(3,4) and then read out the ancilla in a single shot. This procedure realizes a disturbance-free projective measurement of the single spin at a rate two orders of magnitude faster than its relaxation. The QND nature of the measurement protocol(5,6) enables enhancement of the overall measurement fidelity by repeating the protocol. We demonstrate a monotonic increase of the fidelity over 100 repetitions against arbitrary input states. Our analysis based on statistical inference is tolerant to the presence of the relaxation and dephasing. We further exemplify the QND character of the measurement by observing spontaneous flips (quantum jumps)(7) of a single electron spin. Combined with the high-fidelity control of spin qubits(8-13), these results will allow for various measurement-based quantum state manipulations including quantum error correction protocols(14).
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