We propose an interface between the spin of a photon and the spin of an electron confined in a quantum dot embedded in a microcavity operating in the weak-coupling regime. This interface, based on spin selective photon reflection from the cavity, can be used to construct a CNOT gate, a multiphoton entangler and a photonic Bell-state analyzer. Finally, we analyze experimental feasibility, concluding that the schemes can be implemented with current technology. DOI: 10.1103/PhysRevLett.104.160503 PACS numbers: 03.67.Àa, 42.50.Pq, 78.67.Hc Hybrid quantum information systems hold great promise for the development of quantum communication and computing since they allow exploiting different quantum systems at the best of their potentials. For example, in order to build a quantum network [1], photons are excellent candidates for long-distance transmission while quantum states of matter are preferred for local storage and processing. Hybrid (photon-matter) systems can also be used to effectively enable strong nonlinear interactions between single photons [2][3][4]. Several systems have been identified as candidates for local matter qubits, for example, atoms [5,6], ions [7], superconducting circuits [8,9], and semiconductor quantum dots [10][11][12], and their coupling strengths to optical modes have been investigated.Quantum information protocols based on cavity QED often require the system to operate in the strong-coupling regime [2,[13][14][15], where the vacuum Rabi frequency of the dipole g exceeds both the cavity and dipole decay rates. However, in the bad cavity limit, where g is smaller than the cavity decay rate, the coupling between the radiation and the dipole can drastically change the cavity reflection and transmission properties [16][17][18], allowing quantum information schemes to operate in the weak-coupling regime. We exploit this regime, using spin selective dipole coupling, for a system consisting of a single electron charged self-assembled GaAs=InAs quantum dot in a micropillar resonator [19,20]. The potential of this system has also been recognized in [21]. We first show that this specific system can lead to a quantum CNOT gate with the confined electron spin as the control qubit and the incoming photon spin as the target qubit. We apply the CNOT gate to generate multiphoton entangled states. We then construct a complete two-photon Bell-state analyzer (BSA). Complete deterministic BSA is an important prerequisite for many quantum information protocols like superdense coding, teleportation, or entanglement swapping. It cannot be performed with linear optics only [22], while it can be done using nonlinear optical processes [23] (with low efficiency) or employing measurement-based nonlinearities in nondeterministic schemes [24]. Deterministic complete BSA has been shown in a scheme which is conceptually different from the one presented here, exploiting entanglement in two or more degrees of freedom of two photons [25,26]. We conclude with a discussion on the experimental feasibility of the proposed ...

Single self-assembled InAs quantum dots embedded in GaAs photonic crystal defect cavities are a promising system for cavity quantum electrodynamics experiments and quantum information schemes. Achieving controllable coupling in these small mode volume devices is challenging due to the random nucleation locations of individual quantum dots. We have developed an all optical scheme for locating the position of single dots with sub-10 nm accuracy. Using this method, we are able to deterministically reach the strong coupling regime with a spatial positioning success rate of approximately 70%. This flexible method should be applicable to other microcavity architectures and emitter systems.

We demonstrate a technique to tune the optical properties of micropillar cavities by creating small defects on the sample surface near the cavity region with an intense focused laser beam. Such defects modify strain in the structure, changing the birefringence in a controllable way. We apply the technique to make the fundamental cavity mode polarization-degenerate and to fine tune the overall mode frequencies, as needed for applications in quantum information science.Comment: RevTex, 7 pages, 4 figures (accepted for publication in Applied Physics Letters

We demonstrate a technique for achieving spectral resonance between a polarization-degenerate micropillar cavity mode and an embedded quantum dot transition. Our approach is based on a combination of isotropic and anisotropic tensile strain effected by laser-induced surface defects, thereby providing permanent tuning. Such a technique is a prerequisite for the implementation of scalable quantum information schemes based on solid-state cavity quantum electrodynamics.

We discuss the fine-tuning of the optical properties of self-assembled quantum dots by the strain perturbation introduced by laser-induced surface defects. We show experimentally that the quantum dot transition red-shifts, independently of the actual position of the defect, and that such frequency shift is about a factor five larger than the corresponding shift of a micropillar cavity mode resonance. We present a simple model that accounts for these experimental findings.