- 标题
- 摘要
- 关键词
- 实验方案
- 产品
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Authenticated Controlled Quantum Secure Direct Communication Protocol Based on Five-Particle Brown States
摘要： In this paper a new authenticated quantum protocol aiming to establish a controlled secure direct communication based on five-particle Brown states is proposed. In comparison with previous ones, higher amount of quantum channel capacity is spent for transferring secret information. The controller takes the responsibility of communication after authenticating its identity to parties of communication and keeps its supervision task till end phase of transferring information. The bidirectional authentication method along with eavesdropping check, uses the pre-transmitted identification and hash. The classical XOR operator is used for preventing from eavesdropping by dishonest ones.
关键词： Authentication,Brown entangled state,Controlled quantum secure direct communication,Hash function,Decoy qubits
更新于2025-09-23 15:19:57
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Verifying multipartite entangled Greenberger-Horne-Zeilinger states via multiple quantum coherences
摘要： The ability to generate and verify multipartite entanglement is an important benchmark for near-term quantum devices. We develop a scalable entanglement metric based on multiple quantum coherences and demonstrate experimentally on a 20-qubit superconducting device. We report a state fidelity of 0.5165 ± 0.0036 for an 18-qubit GHZ state, indicating multipartite entanglement across all 18 qubits. Our entanglement metric is robust to noise and only requires measuring the population in the ground state; it can be readily applied to other quantum devices to verify multipartite entanglement.
关键词： quantum coherence,multipartite entanglement,quantum computing,superconducting qubits,GHZ states
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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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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Semiclassical analysis of dark-state transient dynamics in waveguide circuit QED
摘要： The interaction between superconducting qubits and one-dimensional microwave transmission lines has been studied experimentally and theoretically in the past two decades. In this work, we investigate the spontaneous emission of an initially excited artificial atom which is capacitively coupled to a semi-infinite transmission line, shorted at one end. This configuration can be viewed as an atom in front of a mirror. The distance between the atom and the mirror introduces a time delay in the system, which we take into account fully. When the delay time equals an integer number of atom oscillation periods, the atom converges into a dark state after an initial decay period. The dark state is an effect of destructive interference between the reflected part of the field and the part directly emitted by the atom. Based on circuit quantization, we derive linearized equations of motion for the system and use these for a semiclassical analysis of the transient dynamics. We also make a rigorous connection to the quantum optics system-reservoir approach and compare these two methods to describe the dynamics. We find that both approaches are equivalent for transmission lines with a low characteristic impedance, while they differ when this impedance is higher than the typical impedance of the superconducting artificial atom.
关键词： quantum optics,circuit quantization,spontaneous emission,dark state,superconducting qubits,microwave transmission lines
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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Controlled-Phase Gate Using Dynamically Coupled Cavities and Optical Nonlinearities
摘要： We show that relatively simple integrated photonic circuits have the potential to realize a high fidelity deterministic controlled-phase gate between photonic qubits using bulk optical nonlinearities. The gate is enabled by converting travelling continuous-mode photons into stationary cavity modes using strong classical control fields that dynamically change the effective cavity-waveguide coupling rate. This architecture succeeds because it reduces the wave packet distortions that otherwise accompany the action of optical nonlinearities [J. Shapiro, Phys. Rev. A 73, 062305 (2006); J. Gea-Banacloche, Phys. Rev. A 81, 043823 (2010)]. We show that high-fidelity gates can be achieved with self-phase modulation in χ(3) materials as well as second-harmonic generation in χ(2) materials. The gate fidelity asymptotically approaches unity with increasing storage time for an incident photon wave packet with fixed duration. We also show that dynamically coupled cavities enable a trade-off between errors due to loss and wave packet distortion. Our proposed architecture represents a new approach to practical implementation of quantum gates that is room-temperature compatible and only relies on components that have been individually demonstrated.
关键词： optical nonlinearities,integrated photonic circuits,photonic qubits,quantum gates,controlled-phase gate
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