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Register a new userRapid microwave-only characterization and readout of quantum dots using multiplexed gigahertz-frequency resonators
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Superconducting resonators enable fast characterization and readout of mesoscopic quantum devices. Finding ways to perform measurements of interest on such devices using resonators only is therefore of great practical relevance. We report the experimental investigation of an InAs nanowire multi-quantum dot device by probing GHz resonators connected to the device. First, we demonstrate accurate extraction of the DC conductance from measurements of the high-frequency admittance. Because our technique does not rely on DC calibration, it could potentially obviate the need for DC measurements in semiconductor qubit devices. Second, we demonstrate multiplexed gate sensing and the detection of charge tunneling on microsecond time scales. The GHz detection of dispersive resonator shifts allows rapid acquisition of charge-stability diagrams, as well as resolving charge tunneling in the device with a signal-to-noise ratio of up to 15 in one microsecond. Our measurements show that GHz-frequency resonators may serve as a universal tool for fast tune-up and high-fidelity readout of semiconductor qubits.
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Spins in silicon quantum devices are promising candidates for large-scale quantum computing. Gate-based sensing of spin qubits offers 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 (JPA), 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 (SNR), we estimate that singlet-triplet single-shot readout with an average fidelity of 99.7% could be performed in 1 $mu$s, well-below the requirements for fault-tolerant readout and 30 times faster than without the JPA. Additionally, the JPA allows operation at a lower RF power while maintaining identical SNR. We determine a noise temperature of 200 mK with a contribution from the JPA (25%), cryogenic amplifier (25%) and the resonator (50%), showing routes to further increase the read-out speed.
We characterize a pair of Cooper-pair boxes coupled with a fixed capacitor using spectroscopy and measurements of the ground-state quantum capacitance. We use the extracted parameters to estimate the concurrence, or degree of entanglement between the two qubits. We also present a thorough demonstration of a multiplexed quantum capacitance measurement technique, which is in principle scalable to a large array of superconducting qubits.
Preparation of a specific quantum state is a required step for a variety of proposed practical uses of quantum dynamics. We report an experimental demonstration of optical quantum state preparation in a semiconductor quantum dot with electrical readout, which contrasts with earlier work based on Rabi flopping in that the method is robust with respect to variation in the optical coupling. We use adiabatic rapid passage, which is capable of inverting single dots to a specified upper level. We demonstrate that when the pulse power exceeds a threshold for inversion, the final state is independent of power. This provides a new tool for preparing quantum states in semiconductor dots and has a wide range of potential uses.
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 these methods enable high-performance charge readout in Si/SiGe quantum dots, achieving a fidelity of 99.9% for a measurement time of 1 $mu$s.
Solid-state quantum emitters are excellent sources of on-demand indistinguishable or entangled photons and can host long-lived spin memories, crucial resources for photonic quantum information applications. However, their scalability remains an outstanding challenge. Here we present a scalable technique to multiplex streams of photons from multiple independent quantum dots, on-chip, into a fiber network for use off-chip. Multiplexing is achieved by incorporating a multi-core fiber into a confocal microscope and spatially matching the multiple foci, seven in this case, to quantum dots in an array of deterministically positioned nanowires. First, we report the coherent control of the emission of biexciton-exciton cascade from a single nanowire quantum dot under resonant two-photon excitation. Then, as a proof-of-principle demonstration, we perform parallel spectroscopy on the nanowire array to identify two nearly identical quantum dots at different positions which are subsequently tuned into resonance with an external magnetic field. Multiplexing of background-free single photons from these two quantum dots is then achieved. Our approach, applicable to all types of quantum emitters, can readily be scaled up to multiplex $>100$ quantum light sources, providing a breakthrough in hardware for photonic based quantum technologies. Immediate applications include quantum communication, quantum simulation, and quantum computation.
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