Nondestructive measurement of electron spins in a quantum dot

Abstract

We propose and implement a nondestructive measurement that distinguishes between two-electron spin states in a quantum dot. In contrast to earlier experiments with quantum dots, the spins are left behind in the state corresponding to the measurement outcome. By measuring the spin states twice within a time shorter than the relaxation time T 1 , correlations between the outcomes of consecutive measurements are observed. They disappear as the wait time between measurements becomes comparable to T 1 . The correlation between the postmeasurement state and the measurement outcome is measured to be ϳ90% on average.

Identifying single electron charge sensor events using wavelet edge detection

“…Thresholding, and more sophisticated derivatives of this method, are commonly used to analyze charge sensor signals [4,6,7,13,14,15,20,21,24,30,31,32,34,42]. Below we show that, while both techniques perform well at low noise, wavelet edge detection has much better tolerance to 1/f and low-frequency noise and is 21 also more tolerant to white noise. The wavelet algorithm described below has previously been used to successfully analyze measurements of a Si/SiGe spin qubit with a QPC charge sensor [32].…”

Prospects for Spin-Based Quantum Computing in Quantum Dots

“…As an alternative approach, dispersive readout of spin singlet and triplet states has been demonstrated with an rf resonant circuit coupled to a DQD [178]. Also, readout via spin-dependent tunnel rates has been achieved for the singlet and triplet states in a single QD [37,179,180].…”

“…One may define the readout fidelity for a particular experiment as F = p 0 F 0 + p 1 F 1 = 1 − p 0 e 0→1 − p 1 e 1→0 , where p 0 (p 1 ) is the probability that the system is initially in |0 (|1 ) [148]. Weighting |0 and |1 equally, this results in F = 1 − (e 0→1 + e 1→0 )/2 [37,180]. A more general quantity is the visibility V = 1 − e 0→1 − e 1→0 , which is independent of p 0 and p 1 and presents a lower bound for the readout fidelity in a system [37,108,174,179].…”

Key capacitive parameters for designing single-electron transistor charge sensors

“…In particular, their strong charge sensitivity allows them to be used as charge sensors for reading out spin or charge qubits contained in quantum dots (QDs), 1-5 and also as quantum point contact (QPC) charge sensors. In two-dimensional electron gas (2DEG) systems such as GaAs/AlGaAs and Si/SiGe heterostructures, many experiments have been carried out on QD-QPC structures [6][7][8][9] and some recent studies have focused on the use of QD-SET structures in order to improve the signal-to-noise ratio (SNR) during qubit readout. 10,11 The charge sensitivity of SETs has been investigated theoretically [12][13][14][15][16] and experimentally [17][18][19][20][21][22][23] to evaluate their effectiveness as charge sensors for dc or radio frequency (RF) measurements.…”