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

Abstract

Single-shot read-out 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 timescales reveals quantum jumps of the spin state: we use the experimentally determined waitingtime distribution to characterize the quantum jumps.PACS numbers: 03.67. Lx, 73.21.La, A fundamental difficulty in quantum information processing is the need for isolation of individual quantum systems from their noisy environment on the one hand, and the requirement for information extraction by selective coupling of qubits to classical (noisy) detectors on the other hand [1]. The requisite one-and two-qubit operations, as well as initialization of each qubit can be carried out by using classical out-of-equilibrium external fields, such as lasers or microwaves; the lack of a need for heralding the successful completion of these operations ensures that they can be accomplished in short timescales. In contrast, quantum measurements are typically slow since information extraction by a classical observer is in many cases hindered by the need to protect the qubit from the external fluctuations. While ingenious schemes for fast qubit measurements have been developed, the timescales required for a high fidelity qubit measurement remains at least an order of magnitude longer than those required for coherent operations in practically all quantum information processing schemes [2][3][4]. In the case of spin qubits in optically active quantum dots (QD), the predicament is even more striking since while optical excitation allows for fast turn on/off of light-matter interaction enabling spin read-out, it at the same time allows for an additional fast channel for spin relaxation. In fact, with the exception of a slow coupled QD scheme requiring a designated read-out QD [5], it has not been possible to carry out single-shot spin measurements on isolated optically active spin qubits [6].In this Letter, we overcome the predicament underlying single-shot spin read-out by enhancing the collection efficiency of resonance fluorescence (RF) from spindependent recycling transitions that are ubiquitous to single-electron charged QDs. The photon collection efficiency of 0.45% that we achieve allows us to obtain a single-shot spin read-out fidelity exceeding 80% in a measurement time of 800 ns. This result corresponds to an enhancement of the spin read-out time by almost three orders of magnitude as compared to the prior measurements on coupled QDs [5]. Continuous monitoring of the spin state enabled by single-shot read-out reveals quantum jumps of the observed spin stemming either from the finite T 1 spin lifetime or spin pumping induced by the resonant read-out laser. A theoretical analysis of quantum jumps using the waiting time distribution (W (τ )) was presented ear...

Nanophotonic Quantum Interface for a Single Solid-state Spin

“…Both multi-shot [71,72] and single-shot [73] spin readout has been demonstrated using this technique in the Faraday configuration. But the reported single-shot readout fidelity is only ∼ 82% [73], limited by the collection efficiency of the emitted photons and the imperfect cycling transitions.…”

“…Both multi-shot [71,72] and single-shot [73] spin readout has been demonstrated using this technique in the Faraday configuration. But the reported single-shot readout fidelity is only ∼ 82% [73], limited by the collection efficiency of the emitted photons and the imperfect cycling transitions. In the Faraday geometry, one can also optically measure the spin via the spin-dependent Kerr or Faraday rotation of a detuned laser [74][75][76].…”

“…Both multi-shot [71,72] and single-shot [73] spin readout has been demonstrated for a charged quantum dot with a magnetic field applied in the Faraday configuration, by using resonance fluorescence spectroscopy. But the highest spin readout fidelity reported so far is only ∼ 84%, limited by the imperfect cycling transition caused by the non-radiative decay mechanism for the optical forbidden transitions.…”

Single-shot optical readout of a quantum bit using cavity quantum electrodynamics

“…Both time-averaged 35,36 and single-shot 19 spin readout has been experimentally realized for a charged quantum dot with a magnetic field applied in the Faraday configuration. However realizing single-shot readout operation in Voigt configuration is more desired because this geometry is the prerequisite for all-optical coherent spin manipulation 37,38 .…”

“…Previous studies have demonstrated single-shot readout with resonance fluorescence in a number of qubit systems, including cold Rubidium atoms [11][12][13] , trapped Calcium 14 and Ytterbium 15 ions, nitrogen vacancy centers 16,17 , quantum dot molecules 18 , and singly charged quantum dot spins with a magnetic field applied parallel to their growth direction (Faraday configuration) 19 .…”