Coupling and characterization of a Si/SiGe triple quantum dot array with a microwave resonator

Scaling up spin qubits in silicon-based quantum dots is one of the pivotal challenges in achieving large-scale semiconductor quantum computation.To satisfy the connectivity requirements and reduce the lithographic complexity,utilizing the qubit array structure and the circuit quantum electrodynamics(cQED)architecture together is expected to be a feasible scaling scheme.A triple-quantum dot(TQD)coupled with a superconducting resonator is regarded as a basic cell to demonstrate this extension scheme.In this article,we investigate a system consisting of a silicon TQD and a high-impedance TiN coplanar waveguide(CPW)resonator.The TQD can couple to the resonator via the right double-quantum dot(RDQD),which reaches the strong coupling regime with a charge–photon coupling strength of g0/(2p)=175 MHz.Moreover,we illustrate the high tunability of the TQD through the characterization of stability diagrams,quadruple points(QPs),and the quantum cellular automata(QCA)process.Our results contribute to fostering the exploration of silicon-based qubit integration.

Coherent manipulation of a tunable hybrid qubit via microwave control

Hybrid qubits enable the hybridization of charge and spin degrees of freedom,which provides a way to realize both a relatively long coherence time and rapid qubit manipulation.Here,we use microwave driving to demonstrate the coherent operation of a tunable hybrid qubit,including X-rotation,Z-rotation,and rotation around an arbitrary axis in the X-Y panel of the Bloch sphere.Moreover,the coherence properties of the qubit and its tunability are studied.The measured coherence time of the X-rotation reaches~14.3 ns.While for the Z-rotation,the maximum decoherence time is~5.8 ns due to the larger sensitivity to noise.By employing the Hahn echo sequence to mitigate the influence of the low-frequency noise,we have improved the qubit coherence time from~5.8 ns to~15.0 ns.Our results contribute to a further understanding of the hybrid qubit and a step towards achieving high-fidelity qubit gates in the hybrid qubit.

Micro-scale photon source in a hybrid cQED system

Conerent photon source is an important element that has been widely used in spectroscopy,imaging,detection,and teleportation in quantum optics.However,it is still a challenge to realize micro-scale coherent emitters in semiconductor systems.We report the observation of gain in a cavity-coupled GaAs double quantum dot system with a voltage bias across the device.By characterizing and analyzing the cavity responses to different quantum dot behaviors,we distinguish the microwave photon emission from the signal gain.This study provides a possibility to realize micro-scale amplifiers or coherent microwave photon sources in circuit quantum electrodynamics(cQED) hybrid systems.

Coupling and readout of semiconductor quantum dots with a superconducting microwave resonator

In a circuit quantum electrodynamics(circuit QED) architecture, the microwave resonator could be used to couple and probe qubits. The long-range coupling and information transfer between nonlocal qubits can be performed via photons trapped in a microwave resonator, promising an effective approach for scaling up solid-state qubits. A series of important advances in the hybrid system composed of a microwave resonator and semiconductor qubits have been achieved in recent years. For instance,with applications of high-impedance microwave resonators, the strong coupling regime between charge/spin qubits and a microwave resonator has been reached. Simultaneously, resonator-based dispersive readout and single-shot readout to probe the qubit state have been further improved due to the increase of the coupling strength. Here, we briefly introduce this hybrid system related to the progress and fruits in achieving the strong coupling between charge/spin qubits in double quantum dots(DQDs)and the resonator, the long-range coupling between qubits, and also the applications of the resonator for qubit state readout.