Fast Optical Preparation, Control, and Readout of a Single Quantum Dot Spin

Abstract

We propose and demonstrate the sequential initialization, optical control, and readout of a single spin trapped in a semiconductor quantum dot. Hole spin preparation is achieved through ionization of a resonantly excited electron-hole pair. Optical control is observed as a coherent Rabi rotation between the hole and charged-exciton states, which is conditional on the initial hole spin state. The spin-selective creation of the charged exciton provides a photocurrent readout of the hole spin state. DOI: 10.1103/PhysRevLett.100.197401 PACS numbers: 78.67.Hc, 42.50.Hz, 71.35.Pq The ability to sequentially initialize, control, and readout a single spin is an essential requirement of any spin based quantum information protocol [1]. This has not yet been achieved for promising schemes based on the optical control of semiconductor quantum dots [2]. These schemes seek to combine the picosecond optical gate speeds of excitons [3][4][5][6], with the potential for millisecond coherence times of quantum dot spins [7][8][9], by optically manipulating the spin via the charged exciton. This results in a system where the potential number of operations before coherence loss could be extremely high, in the range 10 4-9 , and in a system compatible with advanced semiconductor device technologies. A number of important milestones have recently been reached, but these focus on the continuous initialization of an electron [10,11] or hole spin [12], detection of a single quantum dot spin [13,14], or optical control of ensembles of 10 6-7 spins [15,16]. In this Letter, we demonstrate sequential triggered ondemand preparation, optical manipulation, and picosecond time-resolved detection of a single hole spin confined to a quantum dot, thus demonstrating an experimental framework for the fast optical manipulation of single spins. This is achieved using a single self-assembled InGaAs quantum dot embedded in a photodiode structure. The hole spin is prepared by ionizing an electron-hole pair created by resonant excitation. A second laser pulse then drives a coherent Rabi oscillation between the hole and positive trion states, which due to Pauli blocking is conditional on the initial hole spin state, key requirements for the optical control of a spin via the trion transition. Because of Pauli blockade, creation of the charged exciton provides a photocurrent readout of the hole spin state.First we will describe the principle of operation. The qubit is represented by the spin states of the heavy hole (J Figure 1 shows an idealized quantum dot, embedded in an n-i-Schottky diode structure. An electric field is applied, such that the electron tunneling rate is much faster than the hole tunneling rate. The experiments use a sequence of two circularly polarized, timeseparated laser pulses, with a time duration shorter than the electron tunneling time, labeled the ''preparation'' and ''control'' pulses. Figure 1 illustrates the steps (a)-(d) involved in the preparation and readout of the hole spin.Preparation.-(a) The circularly polarized prepar...

Hole-spin initialization and relaxation times in InAs/GaAs quantum dots

“…The initialization in the Voigt configuration is three orders of magnitude quicker than in the Faraday configuration, but the fidelity of this latter configuration is greater. Recently, in absence of an applied magnetic field, Ramsay et al 47 have demonstrated the sequential hole-spin initialization by the ionization of a spin-polarized electron-hole pair with an 81% fidelity, and Gerardot et al 13 have also obtained a high fidelity of the spin state initialization for a single hole under cw optical excitation. In the past, Shabaev et al 48 have proposed the initialization of a single electron spin placed in a transverse magnetic field by a combination of circularly polarized optical π pulses, and the authors have predicted a spin polarization of 99% after eight pulses.…”

Antiferromagnetic interaction in coupled CdSe/ZnMnSe quantum dot structures

“…Recent results have demonstrated marked progresses towards realization of fast optical manipulation of single spins in QDs (Ref. 8) and optically effected controlled-phase gate between two solid-state qubits. 9 One way of achieving spin polarized carriers and excitons in QDs is via direct spin injection from an adjacent layer.…”

Towards coherent optical control of a single hole spin: Rabi rotation of a trion conditional on the spin state of the hole

“…Continuous-wave pumping schemes for the high-fidelity preparation of an electron [20], and hole [21] spin have been demonstrated, not only in a Faraday geometry B-field, but also for electron spins in the Voigt geometry B-field needed for optical control [22,23]. Recently, partial [24,25], and full [26] optical control of a single electron spin has been demonstrated. Full optical control of a single spin is achieved when both the occupation, and relative phase of the spin states can be fully controlled, or in other words, from a well defined initial state, any arbitrary spin state can be prepared.…”

“…In this article, we propose and demonstrate the sequential optical preparation, control, and detection of a single hole spin trapped on an InGaAs/GaAs quantum dot [25]. Using a dot embedded in an n-i-Schottky diode structure, hole spin initialization is achieved by creating a spin-polarized electron-hole pair with near unit probability using a picosecond laser pulse with a pulsearea of π, and waiting for the electron to tunnel leaving a spin-polarized hole.…”