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Tunneling statistics for analysis of spin-readout fidelity

S K Gorman (16254092), Y He (7724882), Matthew Gregory House, J G Keizer (16254053), D Keith (13679875), L Fricke (16265474), Samuel James Hile, M A Broome (16254095), M Y Simmons (13619323)

Published Sep 22, 2017• 16 citations
OpenAlex

Abstract

Radio-frequency single-electron transistors (rf-SETs) are very sensitive charge sensors that are promising for spin-state readout in quantum information processing. It would be advantageous to directly couple the rf-SET to a donor atom in a quantum dot, but it is unclear how rf driving of the SET might affect the electronic tunneling dynamics. Combining full counting statistics, tunneling-rate analysis, and autocorrelations, this study shows that rf driving merely introduces an effective temperature broadening. Optimization of single-shot readout fidelity is explained, which keeps this readout technique viable for quantum computing architectures.

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Radio-frequency single-electron transistors (rf-SETs) are very sensitive charge sensors that are promising for spin-state readout in quantum information processing. It would be advantageous to directly couple the rf-SET to a donor atom in a quantum dot, but it is unclear how rf driving of the SET might affect the electronic tunneling dynamics. Combining full counting statistics, tunneling-rate analysis, and autocorrelations, this study shows that rf driving merely introduces an effective temperature broadening. Optimization of single-shot readout fidelity is explained, which keeps this readout technique viable for quantum computing architectures.
Radio-frequency single-electron transistors (rf-SETs) are very sensitive charge sensors that are promising for spin-state readout in quantum information processing. It would be advantageous to directly couple the rf-SET to a donor atom in a quantum dot, but it is unclear how rf driving of the SET might affect the electronic tunneling dynamics. Combining full counting statistics, tunneling-rate analysis, and autocorrelations, this study shows that rf driving merely introduces an effective temperature broadening. Optimization of single-shot readout fidelity is explained, which keeps this readout technique viable for quantum computing architectures.
The radio-frequency single-electron transistor (rf-SET) possesses key requirements necessary for reading out a solid state quantum computer. This work explores the use of the rf-SET as a single-shot readout device in the presence of 1∕f and telegraph charge noise. For a typical spectrum of 1∕f noise we find that high fidelity, single-shot measurements are possible for signals Δq>0.01e. For the case of telegraph noise, we present a cross-correlation measurement technique that uses two rf-SETs to suppress the effect of random switching events on readout. We demonstrate this technique by monitoring the charge state of a metal double dot system on microsecond time scales. Such a scheme will be advantageous in achieving high readout fidelity in a solid-state quantum computer.
We study the radio-frequency single-electron transistor (rf-SET) as a readout device for charge qubits. We measure the charge sensitivity of an rf-SET to be 6.3microe/sqrt[Hz] and evaluate the backaction of the rf-SET on a single Cooper-pair box. This allows us to compare the needed measurement time with the mixing time of the qubit imposed by the measurement. We find that the mixing time can be substantially longer than the measurement time, which would allow readout of the state of the qubit in a single shot measurement.
High-fidelity qubit readout is critical in order to obtain the thresholds needed to implement quantum error-correction protocols and achieve fault-tolerant quantum computing. Large-scale silicon qubit devices will have densely packed arrays of quantum dots with multiple charge sensors that are, on average, farther away from the quantum dots, entailing a reduction in readout fidelities. Here, we present a readout technique that enhances the readout fidelity in a linear SiMOS four-dot array by amplifying correlations between a pair of single-electron transistors, known as a twin SET. By recording and subsequently correlating the twin SET traces as we modulate the dot detuning across a charge transition, we demonstrate a reduction in the charge readout infidelity by over one order of magnitude compared to traditional readout methods. We also study the spin-to-charge conversion errors introduced by the modulation technique and conclude that faster modulation frequencies avoid relaxation-induced errors without introducing significant spin-flip errors, favoring the use of the technique at short integration times. This method not only allows for faster and higher-fidelity qubit measurements but it also enhances the signal corresponding to charge transitions that take place farther away from the sensors, enabling a way to circumvent the reduction in readout fidelities in large arrays of qubits. Published by the American Physical Society 2024
I report an investigation into using an rf Single Electron Transistor (rf-SET) to implement single shot readout of the quantum state of a Cooper pair box. I fabricated Al/AlOx/Al SETs and Cooper pair boxes using e-beam lithography and double-angle evaporation. The devices had typical charging energies of about 1 K and were measured at 30 mK in a dilution refrigerator. I built rf-SETs with an LC resonant circuit integrated on the chip and operating frequencies of 650 MHz and 1.5 GHz. The rf-SETs had a typical bandwidth of 30 MHz and the best achieved charge sensitivity was 8X10-6 erms/(Hz)1/2 at 1.5 GHz. The rf-SETs were used to measure the Coulomb staircase on the Cooper pair box. Measurements of the staircase show features due to quasiparticle poisoning that are dependent on temperature and SET bias. The data was compared to a theory I developed to extend existing theories of quasiparticle poisoning. My model is based on the calculation of tunneling rates to explain observations of parity effects in the Cooper pair box over a wide temperature range. Quantum state control of the Cooper pair box was demonstrated by using fast voltage pulses applied to the gate. Temporal oscillations of charge states and spectroscopy measurements reveal a dephasing time T2=200 ps at 30 mK, for a drive frequency of 30 GHz. The energy relaxation time T1=140 ns was determined from time domain measurements of the decay of the Cooper pair box charge. The fidelity of single shot measurements and the feasibility of this quantum readout scheme based on the results are discussed.
Electron cotunneling in semiconductor quantum dots is a higher-order tunneling mechanism that connects initial and final charge states through energetically inaccessible virtual intermediate configurations. In quantum-dot arrays, such processes can produce simultaneous charge motion across multiple tunnel junctions and enable transitions that would otherwise be suppressed by Coulomb blockade. Here, building on an earlier proof-of-principle demonstration, we investigate radio-frequency (rf)-driven correlated cotunneling and its application to dispersive quantum-dot readout. Using both theoretical modeling and experimental measurements in two different foundry-fabricated silicon devices, we show that an external rf drive can induce correlated cyclic single-electron transitions, resulting in enhanced charge-polarization of the system. We develop a general theoretical framework for rf electron-cascade readout, which exploits cotunneling events in quantum-dot systems with three or more dots to produce a relative signal enhancement, and extend its experimental demonstration to a gate-sensed device architecture. Our results establish the operating principles of rf electron-cascade readout and provide a route to increased dispersive readout fidelity in semiconductor quantum computing architectures.