Optimized electrical control of a Si/SiGe spin qubit in the presence of an induced frequency shift

Takeda, Kenta; Yoneda, Jun; Otsuka, Takeshi; Nakajima, Takashi; Delbecq, Matthieu; Allison, Giles; Hoshi, Yusuke; Usami, Noritaka; Itoh, Kohei M.; Oda, Shunri; Kodera, Tetsuo; Tarucha, Seigo

doi:10.1038/s41534-018-0105-z

Cited by 41 publications

(19 citation statements)

References 32 publications

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“…A fast CX-operation is thus achieved within τ CX,Q1 = 55 ns and τ CX,Q2 = 75 ns, with Q1 and Q2 as the target qubits respectively.As a result of the pulsing, we observe a minor shift in the resonance frequency of both qubits. This was observed before in Si/SiGe quantum dots [35], and we speculate this to be caused by a rectification of the AC microwave signal, leading to a slight change in the exchange interaction between the dots. We compensate the temporary change in resonance frequency by applying phase corrections to all following pulses (see supplementary materials).…”

supporting

confidence: 76%

Fast two-qubit logic with holes in germanium

Hendrickx

Franke

Sammak

et al. 2020

Nature

275

283

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The promise of quantum computation with quantum dots has stimulated widespread research. Still, a platform that can combine excellent control with fast and high-fidelity operation is absent. Here, we show single and two-qubit operations based on holes in germanium. A high degree of control over the tunnel coupling and detuning is obtained by exploiting quantum wells with very low disorder and by working in a virtual gate space. Spin-orbit coupling obviates the need for microscopic elements and enables rapid qubit control with Rabi frequencies exceeding 100 MHz and a singlequbit fidelity of 99.3 %. We demonstrate fast two-qubit CX gates executed within 75 ns and minimize decoherence by operating at the charge symmetry point. Planar germanium thus matured within one year from a material that can host quantum dots to a platform enabling two-qubit logic, positioning itself as a unique material to scale up spin qubits for quantum information.Gate-defined quantum dots were recognized early on as a promising platform for quantum information [1] and a plethora of materials stacks has been investigated as host material. Initial research mainly focused on the low disorder semiconductor gallium arsenide [2,3]. Steady progress in the control and understanding of this system culminated in the initial demonstration and optimization of spin qubit operations [4,5] and the realization of rudimentary analog quantum simulations [6]. However, the omnipresent hyperfine interactions in group III-V materials seriously deteriorate the spin coherence, despite attempts to mitigate this by nuclear polarization [7]. Drastic improvements to the coherence times could be achieved by switching to the group IV semiconductor silicon, in particular when defining spin qubits in isotopically purified host crystal with vanishing concentrations of nonzero nuclear spin [8]. This enabled single qubit rotations with fidelities beyond 99.9% [9] and the execution of two-qubit logic gates with fidelities up to 98% [10-13], underlining the potential of spin qubits for quantum computation. Nevertheless, quantum dots in silicon are often formed at unintended locations and control over the tunnel coupling determining the strength of two-qubit interactions is limited. Moreover, the absence of a sizable spin-orbit coupling for electrons requires the inclusion of microscopic components such as onchip striplines or nanomagnets close to each qubit, which seriously complicates the design of large and dense 2D-structures. This, combined with the limited control over the location and coupling of the dots, remains an outstanding challenge for the scalability of these systems and a platform that can overcome these limitations would be highly desirable. * These two authors contributed equally to this work Hole states in semiconductors typically exhibit strong spinorbit coupling, which has enabled the demonstration of fast single qubit rotations [14,15] and additionally, unlike electrons, holes do not suffer from nearby valley states. In silicon, unfavorable band alignment...

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supporting

confidence: 76%

Fast two-qubit logic with holes in germanium

Hendrickx

Franke

Sammak

et al. 2020

Nature

275

283

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“…During a square gate-voltage pulse for a duration t CZ at a symmetric operation point, the ancilla spin acquires a qubit-state-dependent phase due to enhanced exchange coupling 3,15 . A Hahn echo sequence converts this phase to the ancilla spin polarization, in a robust manner against a slow drift of the ancilla precession frequency and the qubitstate-independent phase induced by the square gate-voltage pulse (~20π per μs) and the microwave bursts (~0.16π) 16,17 . We extract the qubit-dependent phase shift by changing the prepared qubit state by the microwave burst time t b (Fig.…”

Section: Resultsmentioning

confidence: 99%

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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“…Of the physical platforms available, spin-based quantum bits (qubits) in semiconductors are particularly promising [5,6]. Single-qubit gates with fidelities above 99.9% [7] and two-qubit gate fidelities up to 98% [8,9] have been demonstrated. Spin qubits in silicon are considered a strong candidate for realizing a large-scale quantum processor due to the small qubit dimensions, the localized nature of the control, the CMOS compatibility, the long coherence times [10], and the possibility of operating beyond 1 K [11,12].…”

Section: Introductionmentioning

confidence: 99%

Radio-Frequency Reflectometry in Silicon-Based Quantum Dots

et al. 2021

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Radio-frequency (rf) reflectometry offers a fast and sensitive method for charge sensing and spin readout in gated quantum dots. We focus in this work on the implementation of rf readout in accumulation-mode gate-defined quantum dots, where the large parasitic capacitance poses a challenge. We describe and test two methods for mitigating the effect of the parasitic capacitance, one by on-chip modifications and a second by off-chip changes. We demonstrate that on-chip modifications enable high-performance charge readout in Si/Si x Ge 1−x quantum dots, achieving a fidelity of 99.9% for a measurement time of 1 μs.

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Optimized electrical control of a Si/SiGe spin qubit in the presence of an induced frequency shift

Cited by 41 publications

References 32 publications

Fast two-qubit logic with holes in germanium

Fast two-qubit logic with holes in germanium

Quantum non-demolition readout of an electron spin in silicon

Radio-Frequency Reflectometry in Silicon-Based Quantum Dots

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