- 标题
- 摘要
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- 实验方案
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Quantum Dots via rf Reflectometry
摘要： Silicon spin qubits show great promise as a scalable qubit platform for fault-tolerant quantum computing. However, fast high-fidelity readout of charge and spin states, which is required for quantum error correction, has remained elusive. Radio-frequency reflectometry enables rapid high-fidelity readout of GaAs spin qubits, but the large capacitances between accumulation gates and the underlying two-dimensional electron gas in accumulation-mode Si quantum-dot devices, as well as the relatively low two-dimensional electron gas mobilities, have made radio-frequency reflectometry challenging in these platforms. In this work, we implement radio-frequency reflectometry in a Si/Si-Ge quantum-dot device with overlapping gates by making minor device-level changes that eliminate these challenges. We demonstrate charge-state readout with a fidelity above 99.9% in an integration time of 300 ns. We measure the singlet and triplet states of a double quantum dot via both conventional Pauli spin blockade and a charge latching mechanism, and we achieve maximum fidelities of 82.9 and 99.0% in 2.08- and 1.6-μs integration times, respectively. We also use radio-frequency reflectometry to perform single-shot readout of single-spin states via spin-selective tunneling in microsecond-scale integration times.
关键词： quantum computing,Silicon spin qubits,spin-state readout,charge-state readout,radio-frequency reflectometry
更新于2025-09-23 15:19:57
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Single-photon emission from single-electron transport in a SAW-driven lateral light-emitting diode
摘要： The long-distance quantum transfer between electron-spin qubits in semiconductors is important for realising large-scale quantum computing circuits. Electron-spin to photon-polarisation conversion is a promising technology for achieving free-space or fibre-coupled quantum transfer. In this work, using only regular lithography techniques on a conventional 15 nm GaAs quantum well, we demonstrate acoustically-driven generation of single photons from single electrons, without the need for a self-assembled quantum dot. In this device, a single electron is carried in a potential minimum of a surface acoustic wave (SAW) and is transported to a region of holes to form an exciton. The exciton then decays and creates a single optical photon within 100 ps. This SAW-driven electroluminescence, without optimisation, yields photon antibunching with g(2)(0) = 0.39 ± 0.05 in the single-electron limit (g(2)(0) = 0.63 ± 0.03 in the raw histogram). Our work marks the first step towards electron-to-photon (spin-to-polarisation) qubit conversion for scaleable quantum computing architectures.
关键词： quantum computing,GaAs quantum well,electron-spin qubits,surface acoustic wave,single-photon emission
更新于2025-09-23 15:19:57
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Theory of valley-resolved spectroscopy of a Si triple quantum dot coupled to a microwave resonator
摘要： We theoretically study a silicon triple quantum dot (TQD) system coupled to a superconducting microwave resonator. The response signal of an injected probe signal can be used to extract information about the level structure by measuring the transmission and phase shift of the output field. This information can further be used to gain knowledge about the valley splittings and valley phases in the individual dots. Since relevant valley states are typically split by several μeV, a finite temperature or an applied external bias voltage is required to populate energetically excited states. The theoretical methods in this paper include a capacitor model to fit experimental charging energies, an extended Hubbard model to describe the tunneling dynamics, a rate equation model to find the occupation probabilities, and an input–output model to determine the response signal of the resonator.
关键词： quantum dots,hybrid quantum systems,spin qubits,valley,silicon,cavity QED
更新于2025-09-23 15:19:57
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Spin-photon module for scalable network architecture in quantum dots
摘要： Reliable information transmission between spatially separated nodes is fundamental to a network architecture for scalable quantum technology. Spin qubit in semiconductor quantum dots is a promising candidate for quantum information processing. However, there remains a challenge to design a practical path from the existing experiments to scalable quantum processor. Here we propose a module consisting of spin singlet-triplet qubits and single microwave photons. We show a high degree of control over interactions between the spin qubit and the quantum light field can be achieved. Furthermore, we propose preparation of a shaped single photons with an efficiency of 98%, and deterministic quantum state transfer and entanglement generation between remote nodes with a high fidelity of 90%. This spin-photon module has met the threshold of particular designed error-correction protocols, thus provides a feasible approach towards scalable quantum network architecture.
关键词： quantum dots,spin qubits,quantum network,microwave photons,quantum state transfer
更新于2025-09-23 15:19:57
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Coherence of a Driven Electron Spin Qubit Actively Decoupled from Quasistatic Noise
摘要： The coherence of electron spin qubits in semiconductor quantum dots suffers mostly from low-frequency noise. During the past decade, efforts have been devoted to mitigate such noise by material engineering, leading to substantial enhancement of the spin dephasing time for an idling qubit. However, the role of the environmental noise during spin manipulation, which determines the control fidelity, is less understood. We demonstrate an electron spin qubit whose coherence in the driven evolution is limited by high-frequency charge noise rather than the quasistatic noise inherent to any semiconductor device. We employ a feedback-control technique to actively suppress the latter, demonstrating a π-flip gate fidelity as high as 99.04 (cid:1) 0.23% in a gallium arsenide quantum dot. We show that the driven-evolution coherence is limited by the longitudinal noise at the Rabi frequency, whose spectrum resembles the 1=f noise observed in isotopically purified silicon qubits.
关键词： gallium arsenide quantum dot,low-frequency noise,Rabi frequency,1=f noise,semiconductor quantum dots,π-flip gate fidelity,isotopically purified silicon qubits,feedback-control technique,high-frequency charge noise,electron spin qubits
更新于2025-09-19 17:13:59
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Quantum Dot
摘要： Valley splitting is a key feature of silicon-based spin qubits. Quantum dots in Si/SixGe1?x heterostructures reportedly suffer from a relatively low valley splitting, limiting the operation temperature and the scalability of such qubit devices. Here, we demonstrate a robust and large valley splitting exceeding 200 μeV in a gate-defined single quantum dot, hosted in molecular-beam-epitaxy-grown 28Si/SixGe1?x. The valley splitting is monotonically and reproducibly tunable up to 15% by gate voltages, originating from a 6-nm lateral displacement of the quantum dot. We observe static spin relaxation times T1 > 1 s at low magnetic fields in our device containing an integrated nanomagnet. At higher magnetic fields, T1 is limited by the valley hotspot and by phonon noise coupling to intrinsic and artificial spin-orbit coupling, including phonon bottlenecking.
关键词： valley splitting,spin relaxation,spin qubits,molecular-beam-epitaxy,silicon,quantum dot
更新于2025-09-19 17:13:59
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Coherent spin control of s-, p-, d- and f-electrons in a silicon quantum dot
摘要： Once the periodic properties of elements were unveiled, chemical behaviour could be understood in terms of the valence of atoms. Ideally, this rationale would extend to quantum dots, and quantum computation could be performed by merely controlling the outer-shell electrons of dot-based qubits. Imperfections in semiconductor materials disrupt this analogy, so real devices seldom display a systematic many-electron arrangement. We demonstrate here an electrostatically confined quantum dot that reveals a well defined shell structure. We observe four shells (31 electrons) with multiplicities given by spin and valley degrees of freedom. Various fillings containing a single valence electron—namely 1, 5, 13 and 25 electrons—are found to be potential qubits. An integrated micromagnet allows us to perform electrically-driven spin resonance (EDSR), leading to faster Rabi rotations and higher fidelity single qubit gates at higher shell states. We investigate the impact of orbital excitations on single qubits as a function of the dot deformation and exploit it for faster qubit control.
关键词： Rabi oscillations,silicon quantum dot,spin qubits,electrically-driven spin resonance,quantum dots
更新于2025-09-19 17:13:59
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Complete state tomography of a quantum dot spin qubit
摘要： Semiconductor quantum dots are probably the preferred choice for interfacing anchored matter spin qubits and flying photonic qubits. While full tomography of a flying qubit or light polarization is, in general, straightforward, matter spin tomography is a challenging and resource-consuming task. Here we present an all-optical method for conducting full tomography of quantum dot confined spins. Our method is applicable for electronic spin configurations such as the conduction-band electron and the valence-band hole and for electron-hole pairs such as the bright and dark excitons. We excite the spin qubit using a short, resonantly tuned, polarized optical pulse, which coherently converts the qubit to an excited qubit that decays by emitting a polarized single photon. We perform the tomography by using two different orthogonal, linearly polarized excitations, followed by time-resolved measurements of the degree of circular polarization of the emitted light from the decaying excited qubit. We demonstrate our method on the dark exciton spin state with a fidelity of 0.94, mainly limited by the accuracy of our polarization analyzers.
关键词： spin qubits,tomography,optical methods,dark exciton,quantum dots
更新于2025-09-19 17:13:59
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Fast Gate-Based Readout of Silicon Quantum Dots Using Josephson Parametric Amplification
摘要： Spins in silicon quantum devices are promising candidates for large-scale quantum computing. Gate-based sensing of spin qubits offers a compact and scalable readout with high fidelity, however, further improvements in sensitivity are required to meet the fidelity thresholds and measurement timescales needed for the implementation of fast feedback in error correction protocols. Here, we combine radio-frequency gate-based sensing at 622 MHz with a Josephson parametric amplifier, that operates in the 500–800 MHz band, to reduce the integration time required to read the state of a silicon double quantum dot formed in a nanowire transistor. Based on our achieved signal-to-noise ratio, we estimate that singlet-triplet single-shot readout with an average fidelity of 99.7% could be performed in 1 μs, well below the requirements for fault-tolerant readout and 30 times faster than without the Josephson parametric amplifier. Additionally, the Josephson parametric amplifier allows operation at a lower radio-frequency power while maintaining identical signal-to-noise ratio. We determine a noise temperature of 200 mK with a contribution from the Josephson parametric amplifier (25%), cryogenic amplifier (25%) and the resonator (50%), showing routes to further increase the readout speed.
关键词： quantum computing,spin qubits,gate-based sensing,silicon quantum dots,Josephson parametric amplification
更新于2025-09-19 17:13:59
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Electrons in Solids (Mesoscopics, Photonics, Quantum Computing, Correlations, Topology) || 4. Correlated electrons in complex transition metal oxides
摘要： In the previous chapters of this book, we have discussed the consequences of quantum mechanics on the properties of solid state electrons mostly on the single or two particle level. This revealed the important influence of the phase of the electronic wave functions in mesoscopic electronic transport and a general understanding of the optical properties of solids, where the interaction between the electrons led only to relatively simple modifications such as the excitonic binding energy ERyd,X or the dielectric constant of the material ε. In addition, we have learned how to gain an unprecedented control of the quantum mechanical properties, including the dynamics, for single-electron and two-electron systems in spin qubits or in many-particle states in superconducting qubits. There, the electron-electron interaction was mostly used as an exchange coupling or as a classical repulsive energy for read-out.
关键词： spin qubits,electron-electron interaction,mesoscopic electronic transport,excitonic binding energy,superconducting qubits,dielectric constant,solid state electrons,quantum mechanics,optical properties of solids
更新于2025-09-16 10:30:52