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Entanglement Generation in Superconducting Qubits Using Holonomic Operations
摘要： We investigate a nonadiabatic holonomic operation that enables us to entangle two fixed-frequency superconducting transmon qubits attached to a common bus resonator. Two coherent microwave tones are applied simultaneously to the two qubits and drive transitions between the first excited resonator state and the second excited state of each qubit. The cyclic evolution within this effective three-level Λ-type system gives rise to a holonomic operation entangling the two qubits. Two-qubit states with 95% fidelity, limited mainly by charge noise of the current device, are created within 213 ns. This scheme is a step toward implementation of a SWAP-type gate directly in an all-microwave controlled hardware platform. By extending the available set of two-qubit operations in the fixed-frequency qubit architecture, the proposed scheme may find applications in near-term quantum applications using variational algorithms to efficiently create problem-specific trial states. We illustrate this point by computing the ground state of molecular hydrogen using the holonomic operation.
关键词： holonomic operations,microwave control,entanglement,quantum computing,superconducting qubits
更新于2025-09-23 15:23:52
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Quantum computing with neutral atoms
摘要： The power of quantum computation derives from algorithmic methods that exploit the availability of quantum superposition and entanglement to perform computations that are intractable with classical devices. The race is on to develop hardware that will unleash the promise of quantum algorithms. A handful of different types of hardware are currently being developed with the greatest efforts directed at superconducting, quantum-dot, trapped-ion, photonic, and neutral-atom approaches [1]. While all approaches have strengths and weaknesses, and are at different stages of development, the challenge of creating a practical design that can be scaled to a million or more qubits has not yet been met with any of the existing platforms.
关键词： neutral atoms,Rydberg states,Quantum computing,quantum error correction,qubits
更新于2025-09-23 15:21:21
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Demonstration of Controlled-Phase Gates between Two Error-Correctable Photonic Qubits
摘要： To realize fault-tolerant quantum computing, it is necessary to store quantum information in logical qubits with error correction functions, realized by distributing a logical state among multiple physical qubits or by encoding it in the Hilbert space of a high-dimensional system. Quantum gate operations between these error-correctable logical qubits, which are essential for implementation of any practical quantum computational task, have not been experimentally demonstrated yet. Here we demonstrate a geometric method for realizing controlled-phase gates between two logical qubits encoded in photonic fields stored in cavities. The gates are realized by dispersively coupling an ancillary superconducting qubit to these cavities and driving it to make a cyclic evolution depending on the joint photonic state of the cavities, which produces a conditional geometric phase. We first realize phase gates for photonic qubits with the logical basis states encoded in two quasiorthogonal coherent states, which have important implications for continuous-variable-based quantum computation. Then we use this geometric method to implement a controlled-phase gate between two binomially encoded logical qubits, which have an error-correctable function.
关键词： error correction,quantum computing,logical qubits,geometric phase,controlled-phase gates
更新于2025-09-23 15:21:01
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Autonomous Tuning and Charge-State Detection of Gate-Defined Quantum Dots
摘要： Defining quantum dots in semiconductor-based heterostructures is an essential step in initializing solid-state qubits. With growing device complexity and increasing number of functional devices required for measurements, a manual approach to finding suitable gate voltages to confine electrons electrostatically is impractical. Here, we implement a two-stage device characterization and dot-tuning process, which first determines whether devices are functional and then attempts to tune the functional devices to the single or double quantum-dot regime. We show that automating well-established manual-tuning procedures and replacing the experimenter’s decisions by supervised machine learning is sufficient to tune double quantum dots in multiple devices without premeasured input or manual intervention. The quality of measurement results and charge states are assessed by four binary classifiers trained with experimental data, reflecting real device behavior. We compare and optimize eight models and different data preprocessing techniques for each of the classifiers to achieve reliable autonomous tuning, an essential step towards scalable quantum systems in quantum-dot-based qubit architectures.
关键词： semiconductor qubits,autonomous tuning,machine learning,quantum dots
更新于2025-09-23 15:21:01
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<i>Ab Initio</i> Spin-Strain Coupling Parameters of Divacancy Qubits in Silicon Carbide
摘要： Cubic silicon carbide is an excellent platform for integration of defect qubits into established wafer-scale device architectures for quantum information and sensing applications, where a divacancy qubit, which is similar to the negatively charged nitrogen-vacancy (NV) center in diamond, has favorable coherence properties. We demonstrate by means of density-functional-theory calculations that for most types of distortion the 3C divacancy exhibits slightly smaller spin-strain coupling parameters but greater spin-stress coupling parameters in comparison with the diamond NV. We predict that high-quality 3C-SiC thin films hosting divacancy qubits are prospective platforms for quantum-enhanced pressure-sensor devices.
关键词： spin-strain coupling,quantum sensing,density-functional theory,divacancy qubits,silicon carbide
更新于2025-09-23 15:21:01
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Toward Valleya??Coupled Spin Qubits
摘要： The bid for scalable physical qubits has attracted many possible candidate platforms. In particular, spin-based qubits in solid-state form factors are attractive as they could potentially benefit from processes similar to those used for conventional semiconductor processing. However, material control is a significant challenge for solid-state spin qubits as residual spins from substrate, dielectric, electrodes, or contaminants from processing contribute to spin decoherence. In the recent decade, valleytronics has seen a revival due to the discovery of valley-coupled spins in monolayer transition metal dichalcogenides. Such valley-coupled spins are protected by inversion asymmetry and time reversal symmetry and are promising candidates for robust qubits. In this report, the progress toward building such qubits is presented. Following an introduction to the key attractions in fabricating such qubits, an up-to-date brief is provided for the status of each key step, highlighting advancements made and/or outstanding work to be done. This report concludes with a perspective on future development highlighting major remaining milestones toward scalable spin-valley qubits.
关键词： valleytronics,qubits,quantum information,transition metal dichalcogenides,quantum dots
更新于2025-09-23 15:21:01
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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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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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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