Observation of Quantum Jumps of a Single Quantum Dot Spin Using Submicrosecond Single-Shot Optical Readout

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Observation of Quantum Jumps of a Single Quantum Dot Spin Using Submicrosecond Single-Shot Optical Readout

Aymeric Delteil, Wei-bo Gao, Parisa Fallahi, Javier Miguel-Sanchez, and Atac Imamoğlu

Phys. Rev. Lett. 112, 116802 – Published 19 March 2014

Abstract

Single-shot readout of individual qubits is typically the slowest process among the elementary single- and two-qubit operations required for quantum information processing. Here, we use resonance fluorescence from a single-electron charged quantum dot to read out the spin-qubit state in 800 nanoseconds with a fidelity exceeding 80%. Observation of the spin evolution on longer time scales reveals quantum jumps of the spin state: we use the experimentally determined waiting-time distribution to characterize the quantum jumps.

Received 31 October 2013

DOI:https://doi.org/10.1103/PhysRevLett.112.116802

Authors & Affiliations

Aymeric Delteil, Wei-bo Gao, Parisa Fallahi, Javier Miguel-Sanchez, and Atac Imamoğlu

Institute of Quantum Electronics, ETH Zurich, CH-8093 Zurich, Switzerland

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Vol. 112, Iss. 11 — 21 March 2014

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Images

Figure 1
(a) Pulse sequence used in the plateau scan as well as in the single-shot experiment. The two laser pulses have the same time duration. (b) The resonance fluorescence (RF) counts as a function of gate voltage and laser wavelength of laser 1. Here the RF counts include the total counts detected during both pulses. The magnetic field we use is 2 T and the wavelength of laser 2 is fixed at 961.795 nm. In the middle of the plateau, the signal disappears due to spin pumping except when the laser 1 wavelength is at 961.635 nm or 961.745 nm (marked with red lines) at a gate voltage $\sim 0.236 V$ . At these two wavelengths, the corresponding energy level diagram is shown in (c) and (d), respectively.
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Figure 2
(a) The time-resolved average RF counts measured with two lasers as shown in the energy level diagram in Fig. 1. The time range used to calculate the photon number probability in (c) is shown in the grey area. (b) Spin-flip rate as a function of the excitation laser power in the readout pulse. The saturation power is indicated by the dashed blue line. The error bars are smaller than the symbols, and the deviation from the exponential shape (red line) comes from laser-power-dependent dynamical nuclear spin polarization effects. (c) The normalized probability of photon number detected in a time range of 800 ns after the spin is prepared to the $| ↑ ⟩$ (black column) or $| ↓ ⟩$ (red column). The statistics are obtained from data in 10 seconds (618 000 repetitions). (d) The average number of detected photons for spin-up and spin-down state as a function of the readout duration. (e) The probability of detecting spin up and spin down, and the overall fidelity as a function of the readout duration. The error bar is smaller than the symbols.
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Figure 3
(a) Quantum jumps in continuous readout. The power of laser used for exciting the diagonal transition is weaker for the upper panel ( $P_{a}$ ) and stronger for the lower panel ( $P_{b} > P_{a}$ ). (b) Same data as (a), lower panel, but the counts are stored in $1 μ s$ bins. (c) Second-order correlation function $g^{(2)} (t)$ (black trace) and waiting time distribution (red trace) for the data in the upper panel of (a). The dashed line shows the spin lifetime. Inset: the normalized waiting time function for the upper panel (red line) and the lower panel (blue line) in (a). Two exponential decays are observed. The fitted decay times for the red line are $t_{wait} = 349 \pm 5 ns$ and $t_{repump} = 12.1 \pm 0.3 μ s$ and for the blue line $t_{wait} = 371 \pm 5 ns$ and $t_{repump} = 6.32 \pm 0.07 μ s$ .
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