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arXiv:2504.05016

Radio frequency single electron transmission spectroscopy of a semiconductor Si/SiGe quantum dot

Imri Fattal, Jacques Van Damme, Bart Raes, Clément Godfrin, Gulzat Jaliel, Ke‐Qiu Chen, Thomas Van Caekenberghe, Arne Loenders, Kubicek, S., Shana Massar, Yann Canvel, Julien Jussot, Yosuke Shimura, Roger Loo, Wan, D., Massimo Mongillo, Kristiaan De Greve

Published Apr 7, 2025• 0 citations
arXivHTMLPDF

Abstract

Rapid single shot spin readout is a key ingredient for fault tolerant quantum computing with spin qubits. An RF-SET (radio-frequency single electron transistor) is predominantly used as its the readout timescale is far shorter than the spin decoherence time. In this work, we experimentally demonstrate a transmission-based RF-SET using a multi-module semiconductor-superconductor assembly. A monolithically integrated SET placed next to a double quantum dot in a Si/SiGe heterostructure is wire-bonded to a superconducting niobium inductor forming the impedance-transforming network. Compared to RF reflectometry, the proposed set-up is experimentally simpler without the need for directional couplers. Read-out performance is benchmarked by the signal-to-noise (SNR) of a dot-reservoir transition (DRT) and an interdot charge transition (ICT) in the double quantum dot near the SET as a function of RF power and integration time. The minimum integration time for unitary SNR is found to be 100 ns for ICT and 300 ns for DRT. The obtained minimum integration times are comparable to the state of the art in conventional RF reflectometry set-ups. Furthermore, we study the turn-on properties of the RF-SET to investigate capacitive shifts and RF losses. Understanding these effects are crucial for further optimisations of the impedance transforming network as well as the device design to assist RF read-out. This new RF read-out scheme also shows promise for multiplexing spin-qubit readout and further studies on rapid charge dynamics in quantum dots.

DOI
10.48550/arxiv.2504.05016

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Rapid single shot spin readout is a key ingredient for fault tolerant quantum computing with spin qubits. An RF-SET (radio-frequency single electron transistor) is predominantly used as its the readout timescale is far shorter than the spin decoherence time. In this work, we experimentally demonstrate a transmission-based RF-SET using a multi-module semiconductor-superconductor assembly. A monolithically integrated SET placed next to a double quantum dot in a Si/SiGe heterostructure is wire-bonded to a superconducting niobium inductor forming the impedance-transforming network. Compared to RF reflectometry, the proposed set-up is experimentally simpler without the need for directional couplers. Read-out performance is benchmarked by the signal-to-noise (SNR) of a dot-reservoir transition (DRT) and an interdot charge transition (ICT) in the double quantum dot near the SET as a function of RF power and integration time. The minimum integration time for unitary SNR is found to be 100 ns for ICT and 300 ns for DRT. The obtained minimum integration times are comparable to the state of the art in conventional RF reflectometry set-ups. Furthermore, we study the turn-on properties of the RF-SET to investigate capacitive shifts and RF losses. Understanding these effects are crucial for further optimisations of the impedance transforming network as well as the device design to assist RF read-out. This new RF read-out scheme also shows promise for multiplexing spin-qubit readout and further studies on rapid charge dynamics in quantum dots.
We introduce a multimode superconducting inductor architecture that enables radio-frequency reflectometry at multiple discrete frequencies up to 2 GHz, addressing limitations of conventional single-mode designs. The spiral inductor's distributed inter-turn capacitance yields distinct resonant modes with varied impedance-matching conditions. By probing a quantum dot across several modes, we extract tunneling rates over a broad frequency range and identify signatures of nearby charge defects. Using one of the higher-order modes, we demonstrate single-shot spin readout via a radio-frequency single-electron transistor (RF-SET), achieving singlet-triplet readout with an integration time of 8 us and a readout fidelity of 98%. These results establish multimode inductance as a scalable and flexible component for fast spin-qubit readout and device-quality characterization.
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We introduce a multimode superconducting inductor architecture that enables radio frequency reflectometry at multiple discrete frequencies up to 2 GHz, addressing limitations of conventional single-mode designs. The spiral inductor's distributed capacitance yields distinct resonant modes with varied impedance-matching conditions. By probing a quantum dot across several modes, we extract tunneling rates over a broad frequency range and identify signatures of nearby charge defects. Using a higher-order mode of the distributed inductor, rather than the fundamental mode, we demonstrate single-shot spin readout via a radio frequency single-electron transistor (RF-SET), achieving singlet-triplet readout with an integration time of 8 μs and a readout fidelity of 98%. These results establish multimode inductance as a scalable and flexible component for fast spin qubit readout and device-quality characterization.
Frequency-multiplexed radio-frequency (RF) reflectometry is a promising technique for large-scale quantum dot-based qubit systems because it enables simultaneous readout of multiple qubits and helps to reduce the wiring density in peripheral circuits. However, in the conventional L-C-type matching circuits, resonator frequency tunability is limited by poor design flexibility of the shunt capacitance and hence the circuit. Recently, L-L-type matching circuits comprising a series and a shunt inductor have been proposed to address this issue. Here, we report RF reflectometry readout of silicon quantum dot-based charge sensors embedded in L-L-type circuits. We determine the inductance values for target resonance frequencies based on our equivalent circuit model that incorporates the parasitic elements of the inductors and demonstrate resonator frequency tunability of up to 1 GHz with 3-dB resonator bandwidths on the order of MHz. The measured conductance sensitivities, on the order of 10−5(e2/h)/Hz at 4 K, are only moderately dependent on the resonance frequency up to 630 MHz. These results highlight the prospects of L-L-type matching circuits for rapid and multiplex reflectometry readout of semiconductor spin qubits.
By coupling a radio-frequency single-electron transistor (RF-SET) to a quantum dot (QD) in a GaAs/AlGaAs heterostructure, we have succeeded in detecting the tunneling of individual electrons on and off the QD on time scales as short as one microsecond. Using charge detection to probe the state of the QD allows us to nearly isolate the dot from its leads, thereby minimizing decoherence-inducing effects of the environment. We have extended these charge detection techniques to double quantum dots (DQDs) that can simultaneously be used to characterize the backaction of the RF-SET. The combined RF-SET/DQD system is well-suited to the development of charge- or spin-based quantum bits, and to investigation of the quantum measurement problem.
Spin qubits in gate-defined semiconductor quantum dots are a promising platform for realising a scalable quantum computer. This platform encodes quantum information into the intrinsic angular momentum (spin) of individual electrons or holes. In particular, hole spins in quantum dots enable the possibility of all-electrical spin control due to their intrinsic spin-orbit coupling. One important criterion of a quantum computer is the ability to reliably read out the state of the qubit. This is done by mapping spin information to the charge degree of freedom, combined with a method for charge detection. Charge detection can be facilitated by coupling a resonator directly to the quantum dot gate or to a charge sensor and measuring the resonator's phase or amplitude response. In this thesis, we describe a set of experiments relating to the implementation of hole spin qubit readout with superconducting resonators. First, we study gate-based charge sensing in a Si fin field-effect transistor (finFET) device using a superconducting NbN nanowire resonator. We find that the resonator amplifies capacitive crosstalk when electrical control pulses are applied to gate electrodes in this device. This occurs whenever a spectral component of qubit control pulses overlaps with the resonance frequency, which we show may occur for both baseband and radio-frequency (RF) drive signals. We quantify this crosstalk in a transport-based method, and attribute its source to the capacitance between the bondpads of neighbouring gate electrodes. In a second experiment, we use an RF charge sensor with the same nanowire technology to read out hole spin qubits formed in the quantum well of a Ge/SiGe heterostructure. A screening layer approach is used to facilitate RF matching due to large RF dissipation found in the heterostructure. We implement a double-latched readout scheme in this system to reduce errors arising from both spin and charge decay during readout. The spin-to-charge conversion process and its dependence on magnetic field orientation is studied. Spin and charge decay processes arising after spin-to-charge conversion are mitigated by choosing an optimal working point for the field orientation, field amplitude and readout pulse times. By doing so, we achieve an average single-shot state-preparation-and-measurement fidelity of 97%, primarily bounded by imperfect state preparation and limited signal-to-noise ratio. Finally, we study coplanar waveguide resonators fabricated from NbN. We investigate the feasibility of integrating this type of resonator onto the same chip as the Si finFET quantum dots. We then develop a novel resonator readout technique by the interference of two microwave sidebands. We demonstrate the insensitivity of this technique to common-mode phase and amplitude noise both theoretically and experimentally. This technique is then used to study resonator noise arising from two-level system defects. These results highlight both the practical constraints and the potential for achieving high readout fidelities using resonator-based hole spin qubit readout. This work establishes a blueprint for mitigating resonator-induced crosstalk and enabling high-fidelity readout in lossy materials by incorporating a screening layer.