Quantum non-demolition measurement of an electron spin qubit

Nakajima, Takashi; Noiri, Akito; Yoneda, Jun; Delbecq, Matthieu; Stano, Peter; Otsuka, Takeshi; Takeda, Kenta; Amaha, S.; Allison, Giles; Kawasaki, Kento; Ludwig, Arne; Wieck, A. D.; Loss, Daniel; Tarucha, Seigo

doi:10.1038/s41565-019-0426-x

Cited by 83 publications

(68 citation statements)

References 30 publications

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“…This is limited by a relatively short electron spin lifetime, compared with single nuclear spins in silicon where 99.8% readout fidelity is achieved as a result of >99.98% non-demolition fidelity 19,20 . We note that, while both F M and F P are successfully improved by the cumulative QND readout, the observed F QND falls short of our earlier expectations 18 and the overall QND performance is impacted by this. The ratio T # 1 =T " 1 ¼ 31 is deviated from the ideal thermal population ratio (=16) between the Zeeman sublevels at the electron temperature (~50 mK), and the measured T "…”

Section: Discussioncontrasting

confidence: 88%

“…We separate the error in the prepared qubit spin state (during the process of initialization, rotation, and preceding ancilla measurements) from the measurement infidelity 18 by expressing the joint probability P(m i m 30 ) as Supplementary Fig. 2).…”

Section: Resultsmentioning

confidence: 99%

“…, and g # " ð Þ i as fitting parameters, assuming that p # iÀ1 is an exponentially decaying Rabi oscillation 11 , similarly to ref. 18 . We then model the i-dependence of…”

Section: Methodsmentioning

confidence: 99%

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Quantum non-demolition readout of an electron spin in silicon

et al. 2020

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While single-shot detection of silicon spin qubits is now a laboratory routine, the need for quantum error correction in a large-scale quantum computing device demands a quantum non-demolition (QND) implementation. Unlike conventional counterparts, the QND spin readout imposes minimal disturbance to the probed spin polarization and can therefore be repeated to extinguish measurement errors. Here, we show that an electron spin qubit in silicon can be measured in a highly non-demolition manner by probing another electron spin in a neighboring dot Ising-coupled to the qubit spin. The high non-demolition fidelity (99% on average) enables over 20 readout repetitions of a single spin state, yielding an overall average measurement fidelity of up to 95% within 1.2 ms. We further demonstrate that our repetitive QND readout protocol can realize heralded high-fidelity (>99.6%) groundstate preparation. Our QND-based measurement and preparation, mediated by a second qubit of the same kind, will allow for a wide class of quantum information protocols with electron spins in silicon without compromising the architectural homogeneity.

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Section: Discussioncontrasting

confidence: 88%

Section: Resultsmentioning

confidence: 99%

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Quantum non-demolition readout of an electron spin in silicon

et al. 2020

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“…Naively, one expects that continuous, perfect monitoring will rapidly purify the system; however, it is known from the study of quantum-error-correcting codes that quantum states can be protected from extensive numbers of local measurements [12][13][14]. Recently, there has been significant experimental progress towards realizing the requisite ingredients for such measurement-driven purification of manybody states in quantum computing platforms [15][16][17][18][19][20][21][22][23][24].…”

Section: Introductionmentioning

confidence: 99%

Dynamical Purification Phase Transition Induced by Quantum Measurements

2020

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Continuously monitoring the environment of a quantum many-body system reduces the entropy of (purifies) the reduced density matrix of the system, conditional on the outcomes of the measurements. We show that, for mixed initial states, a balanced competition between measurements and entangling interactions within the system can result in a dynamical purification phase transition between (i) a phase that locally purifies at a constant system-size-independent rate and (ii) a "mixed" phase where the purification time diverges exponentially in the system size. The residual entropy density in the mixed phase implies the existence of a quantum error-protected subspace, where quantum information is reliably encoded against the future nonunitary evolution of the system. We show that these codes are of potential relevance to fault-tolerant quantum computation as they are often highly degenerate and satisfy optimal trade-offs between encoded information densities and error thresholds. In spatially local models in 1 þ 1 dimensions, this phase transition for mixed initial states occurs concurrently with a recently identified class of entanglement phase transitions for pure initial states. The purification transition studied here also generalizes to systems with long-range interactions, where conventional notions of entanglement transitions have to be reformulated. We numerically explore this transition for monitored random quantum circuits in 1 þ 1 dimensions and all-to-all models. Unlike in pure initial states, the mutual information of an initially completely mixed state in 1 þ 1 dimensions grows sublinearly in time due to the formation of the error-protected subspace. Purification dynamics is likely a more robust probe of the transition in experiments, where imperfections generically reduce entanglement and drive the system towards mixed states. We describe the motivations for studying this novel class of nonequilibrium quantum dynamics in the context of advanced quantum computing platforms and fault-tolerant quantum computation.

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“…Inspired by a theoretical analysis of two-qubit gate implementation employing state-dependent potentials in cold atom systems in optical fiber array [27][28][29], we recently proposed a spin-selective electron transfer method described in [12], which realizes non-local qubit operations in a quantum dot array. This proposal also offers quantum non-demolition measurement of electron spin [30][31][32] provided that the electron position is measured without introducing the dissipation to the electron.…”

Section: Introductionmentioning

confidence: 99%

Theoretical Study on Spin-Selective Coherent Electron Transfer in a Quantum Dot Array

2019

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Recently, we proposed the spin-selective coherent electron transfer in a silicon-quantum-dot array. It requires temporal tuning of two pulses of an oscillating magnetic field and gate voltage control. This paper proposes a simpler method that requires a single pulse of oscillating magnetic field and gate voltage control. We examined the robustness of the control against the error in the pulse amplitude and the effect of the excited states relaxation to the control efficiency. In addition, we propose a novel control method based on a shortcuts-to-adiabaticity protocol, which utilizes two pulses but requires temporal control of the pulse amplitude for only one of them. We compared their efficiencies under the effect of realistic pulse amplitude errors and relaxation.

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Quantum non-demolition measurement of an electron spin qubit

Cited by 83 publications

References 30 publications

Quantum non-demolition readout of an electron spin in silicon

Quantum non-demolition readout of an electron spin in silicon

Dynamical Purification Phase Transition Induced by Quantum Measurements

Theoretical Study on Spin-Selective Coherent Electron Transfer in a Quantum Dot Array

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