A quantum logic gate between a solid-state quantum bit and a photon

Abstract

QDs are robust and spectrally narrow quantum emitters that have attracted significant interest as solid-state qubits. Various approaches have been pursued for storage and manipulation of quantum information in QDs. One approach has been to exploit neutral exciton transitions that can be controlled all-optically to enable both single qubit operations as well as two-qubit operations between distinguishable excitons in a QD 12 .More recently, major progress has been achieved in coherently manipulating highly 2 stable spin states of a charged QD, which promise significantly longer coherence times [13][14][15][16][17] .Another important property of QDs is that they can be coupled to optical nano-cavities in the strong coupling regime 18-21 where a QD can modify the cavity spectral response 22,23 , enabling novel applications such as ultra-fast low photon number optical switching [24][25][26] and single QD lasing 27 . Furthermore, the strong coupling regime can be exploited to interface these solid-state qubits with a flying photonic qubit through direct QD-photon quantum logic operations, as proposed in a number of theoretical works [6][7][8] . In order to realize this capability, three essential requirements must be met. First, the QD must possess two quantum states whose coherence time is long compared to the interaction time with the photonic qubit. Second, the qubit states of the QD must be coherently controllable. Finally, the qubit state of the QD must have a strong effect on the quantum state of the photon. Achieving these requirements in a solid-state photonic platform has remained an outstanding challenge.In this letter we demonstrate that a QD strongly coupled to an optical nanocavity can satisfy all of the above requirements, implementing a solid-state qubit in a cavity system that can perform quantum gates on a photon at picosecond timescales. We experimentally demonstrate a cNOT logic gate between the QD and a photonic qubit, which is a universal quantum operation that can serve as a general light-matter interface for remote entanglements and distributed quantum computation. Our device is composed of an indium arsenide (InAs) QD strongly coupled to a photonic crystal cavity. Fig. 1a illustrates the level structure of an InAs QD, which includes a ground state (|g) and two bright exciton states, labelled |+ and |-, representing the two anti-aligned spin configurations of the electron and hole. The optical transitions from the ground state to the two bright excitons, denoted  + and  -, exhibit right and left circularly polarized emission respectively at high magnetic field. For all measurements performed in this work the biexciton transition is significantly detuned and can therefore be ignored, enabling the QD to be treated as a three-level system. By applying a magnetic field in the sample growth direction (Faraday configuration), the  + transition can be tuned on resonance with the cavity while the  -transition remains detuned 28 . In this configuration, 3 states |g and |- are the qubit stat...

Coherent spin control of a nanocavity-enhanced qubit in diamond

“…Such systems with specific NV-cavity coupling parameters can also be used for high-fidelity readout due to the modification of spin dynamics of cavity-coupled NVs 25 . Our on-chip architecture could be used to efficiently scale NV-nanocavity systems to many quantum memories connected via photons [26][27][28][29] .…”

Two-Photon Interference from the Far-Field Emission of Chip-Integrated Cavity-Coupled Emitters

“…[22][23][24][25] Emitters coupled to cavities can also serve as highly nonlinear devices operating at low photon numbers, 26 as well as efficient interfaces between photons and solid-state quantum memory. 27,28 The majority of the work to-date focused on a single emitter in a cavity, which can exhibit nearly perfect single photon purity and indistinguishability using resonant pumping techniques. [14][15][16][17] Two-photon interference has been demonstrated from two cavity-coupled emitters on different chips contained in separate cryostats.…”

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

“…To explain the robustness, we note that the detuned contributions also suppress the laser induced spin flip. The robustness of the success probability over the emitter spectral diffusion makes this protocol very appealing for experimental realizations in the quantum dot system, since spectral diffusion is the dominant term in the quantum dot linewidth in several reported experiments 25,58 .…”