Dispersive Readout of a Few-Electron Double Quantum Dot with Fast rf Gate Sensors

Abstract

We report the dispersive charge-state readout of a double quantum dot in the few-electron regime using the in situ gate electrodes as sensitive detectors. We benchmark this gate-sensing technique against the well established quantum point contact (QPC) charge detector and find comparable performance with a bandwidth of ∼ 10 MHz and an equivalent charge sensitivity of ∼ 6.3 × 10 −3 e/ √ Hz. Dispersive gate-sensing alleviates the burden of separate charge detectors for quantum dot systems and promises to enable readout of qubits in scaled-up arrays.Non-invasive charge detection has emerged as an important tool for uncovering new physics in nanoscale devices at the single-electron level and allows readout of spin qubits in a variety of material systems [1][2][3][4][5][6][7][8][9]. For quantum dots defined electrostatically by the selective depletion of a two dimensional electron gas (2DEG), the conductance of a proximal quantum point contact (QPC) [4][5][6][7]9] or single electron transistor (SET) [3,8] can be used to detect the charge configuration in a regime where direct transport is not possible. This method can, in principle, reach quantum mechanical limits for sensitivity [10] and has enabled the detection of single electron spin-states [4, 7, 11] with a 98% readout fidelity in a single-shot [12].An alternate approach to charge-state detection, long used in the context of single electron spectroscopy [13], is based on the dispersive signal from shifts in the quantum capacitance [14,15] when electrons undergo tunnelling. Similar dispersive interactions are now the basis for readout in a variety of quantum systems including atoms in an optical resonator [16], superconducting qubits [17][18][19] and nanomechanical devices [20].In this Letter we report dispersive readout of quantum dot devices using the standard, in situ gate electrodes coupled to lumped-element resonators as highbandwidth, sensitive charge-transition sensors.We demonstrate the sensitivity of this gate-sensor in the fewelectron regime, where these devices are commonly operated as charge or spin qubits [21] and benchmark its performance against the well established QPC charge sensor. We find that because the quantum capacitance is sufficiently large in these devices, gate-sensors have similar sensitivity to QPC sensors. In addition, we show that gate-sensors can operate at elevated temperatures in comparison to QPCs.Previous investigations, in the context of circuit quantum electrodynamics (c-QED), have engineered a dispersive interaction between many-electron dots and superconducting coplanar waveguide resonators [22][23][24][25]. Recently, the charge and spin configuration of double quantum dots has also been detected by dispersive changes in a radio frequency resonator coupled directly to the source or drain contacts of the device [25][26][27][28]. The present work advances these previous studies by demonstrating that the gates, already in place to define the quantum dot system, can also act as fast and sensitive readout detectors in the single...

Sensitive Radio-Frequency Measurements of a Quantum Dot by Tuning to Perfect Impedance Matching

“…Since this is about twice the singlet-triplet qubit relaxation time [33] in GaAs, further improvements are required to achieve single-shot readout. Our approach can be improved by optimizing the remaining geometric capacitance in the circuit by using superconducting inductors to increase the quality factor [10,34] and by using a superconducting amplifier with drastically reduced noise temperature [35].…”

“…If the state can be mapped to an electrical impedance, this goal can be achieved using radio-frequency reflectometry of an electrical resonator incorporating the quantum device [1]. This technique permits rapid readout of charge sensors [2,3], spin qubits [4], and nanomechanical resonators [5], as well as complex impedance measurements of quantum-dot circuits [6][7][8][9][10][11]. For optimal sensitivity, which can approach the quantum limit [12], impedance matching between the device and the external circuitry is essential to maximize power transfer between them [13,14].…”

Radio-frequency dispersive detection of donor atoms in a field-effect transistor

“…We attach the matching circuit to the gate because localized states (e.g. donors) that are coupled to both leads as well as inter-channel transition are observable in this way 10,11 . Furthermore, the present configuration is more easily scale-able for practical device applications; Since 'gate-only' sensing is utilized there in no need for strongly tunnel coupled ohmic contacts 10 .…”

A quantitative study of bias triangles presented in chemical potential space

“…These occupation numbers only change when a gate voltage(s) is changed in such a way that the chemical potential of a dot is lowered below that of the leads µ S(D) or that of the neighboring dot. These boundaries between stable charge regions can be experimentally mapped out by measuring a response sensitive to charge reconfigurations in the device, such as a nearby quantum point contact [9] or single electron transistor [10,11] or, as recently shown, the dispersive response of one of the device gates [12]. In this manuscript, however, we measured the transport through the device.…”