Quantum dot spin coherence governed by a strained nuclear environment

Abstract

The interaction between a confined electron and the nuclei of an optically active quantum dot provides a uniquely rich manifestation of the central spin problem. Coherent qubit control combines with an ultrafast spin–photon interface to make these confined spins attractive candidates for quantum optical networks. Reaching the full potential of spin coherence has been hindered by the lack of knowledge of the key irreversible environment dynamics. Through all-optical Hahn echo decoupling we now recover the intrinsic coherence time set by the interaction with the inhomogeneously strained nuclear bath. The high-frequency nuclear dynamics are directly imprinted on the electron spin coherence, resulting in a dramatic jump of coherence times from few tens of nanoseconds to the microsecond regime between 2 and 3 T magnetic field and an exponential decay of coherence at high fields. These results reveal spin coherence can be improved by applying large magnetic fields and reducing strain inhomogeneity.

Quantum Effects in Higher-Order Correlators of a Quantum-Dot Spin Qubit

“…The slowly oscillatory behavior is contrary to predictions of the model with only two lifetimes, but comparable to features observed in spin echo measurements [5,20,31].…”

“…This model disregards feedback of the central spin dynamics on the nuclear spin bath, which was proven to be a good approximation due to strong nuclear quadrupole coupling [5,20,26]. We also disregard transverse Overhauser field components since their effect is suppressed due to fast spin precession in the yz-plane.…”

“…This confirms that the oscillations of g 3 (t, t) at magnetic fields below 4 T can be explained by the presence of quadrupole interactions in the nuclear spin bath, in agreement with Refs. [5,20,31].…”

“…Electronic spins in optically active quantum dots (QDs) have exhibited very long spin lifetimes T 1 , extending beyond a millisecond [1,2], and intrinsic dephasing times T 2 beyond one microsecond when subject to externally applied magnetic fields [3][4][5]. These properties, combined with the potential for ultrafast optical preparation and control [6][7][8], make QD spin qubits very attractive for quantum information processing [9].…”

Phase-tuned entangled state generation between distant spin qubits

“…Matter qubits can be realized using confined electrons [18], heavy holes [19], or dark excitons [20] in these systems. While quantum correlations have been observed between distant heavy hole spins [15], it is the electron that offers the longest coherence time in this system to date [21][22][23].In this Letter, we present optical generation of nonlocal quantum-entangled states between two distant nodes formed by electron spins confined in separate QDs. Through a single-photon state projection protocol [24] and the bright narrow-linewidth emission available from QDs [25], we realize an entanglement generation rate of 7.3 kHz, the highest rate to date.…”