Fig. 1: Complete spin control for versatile spin-photon entanglement.
From: Deterministic and reconfigurable graph state generation with a single solid-state quantum emitter
a Scanning electron micrograph of an electrically contacted QD-micropillar cavity device and a schematic representation of entanglement between QD spin and emitted photons. b Optical selection rules of a negatively charged QD under a small (< 100 mT) transverse magnetic field \({\overrightarrow{B}}_{y}\). LA-phonon assisted excitation is used to excite the QD with a blue detuning of 0.8 nm. The fast (4ps), red-detuned and circularly polarized optical spin rotation pulse (OSRP) induces an AC Stark shift that imprints a phase shift between the \(\left\vert {\uparrow }_{z}\right\rangle\) and \(\left\vert {\downarrow }_{z}\right\rangle\) states, which is equivalent to a coherent rotation about the z-axis. c Spin projection along the z-axis (Sz) as a function of time (and equivalent rotation angle θ), illustrating the coherent Larmor precession undergone by the electron spin for B = 60 mT. d (Left) Spin projection Sz as a function of OSRP power (and equivalent rotation angle φ), demonstrating rotation of the electron spin about the z-axis. The 3-pulse sequence (inset) used to measure Sz is composed of two excitation pulses (labeled LA) and one OSRP with variable power. Error bars are derived from Poissonian statistics. (Right) Equivalent quantum circuit diagram, which features the unitary gate U(θ, φ), we can perform by combining Larmor precession and OSRP. e Representation of spin control in the Bloch sphere. Starting from a measurement of a photon in the R polarization basis, which heralds the spin state in up \({\left\vert \! \uparrow \right\rangle }_{z}\) (marked 0), a 60 mT transverse magnetic field induces a Larmor precession in the xz-plane. After an arbitrary rotation by angle θ, an OSRP rotates the spin about the z-axis with an angle φ.
