We report on the optical investigation of single electron spins bound to fluorine donor impurities in ZnSe. Measurements of photon antibunching establish the presence of single, isolated optical emitters, and magnetooptical studies are consistent with the presence of an exciton bound to the spin-impurity complex. The isolation of this single donor-bound exciton complex and its potential homogeneity offer promising prospects for a scalable semiconductor qubit with an optical interface.PACS numbers: 78.55. Et, Schemes for quantum information processing and quantum communications rely on scalable, robust qubits. In particular, there are many proposals that require fast, efficient, and homogenous single-photon sources 1-3 and still others that rely on the interaction between matter qubits and flying photonic qubits 4 . The requisites for both types of schemes can be satisfied with semiconductor electron spins, which serve as single photon sources 5 or long lived quantum memories with an optical interface 6-8 . However, optical schemes, particularly those based on entanglement, also require large numbers of homogenous photon emitters 9-14 . Electron spins in self-assembled QDs, unfortunately, suffer from large inhomogenities due to their natural size distribution.Impurity-bound electrons in direct bandgap semiconductors, however, have relatively little inhomogeneous broadening 15-20 , yet still possess strong optical transitions when binding an additional exciton 18-21 and long ground state coherence times 7 .An electron bound to a single fluorine donor in ZnSe (F:ZnSe) may serve as a physical qubit with many potential advantages over previously researched qubits. F:ZnSe is particularly appealing because of its nuclear structure compared to III-V-based bound-exciton or quantum dot systems. Unlike III-V systems, isotopic purification of the ZnSe-host matrix to a nuclear-spin-0 background is possible, eliminating magnetic noise from nuclear spin diffusion 22,23 . Further, the F-impurity has a nuclear spin of 1/2 with 100% abundance. Electronnuclear spin swapping schemes 24,25 can be used, which, in combination with the spin-0 background of the isotopically purified host matrix, could lead to an extremely long-lived qubit. Additionally, the applicability of standard microfabrication techniques 26,27 to ZnSe makes the F:ZnSe system particularly scalable.The F:ZnSe system has already shown promise as a scalable source of single photons in Ref. 20. However, a) Electronic address: kdegreve@stanford.edu b) Currently at HRL Laboratories, LLC, 3011 Malibu Canyon Rd., Malibu, CA 90265.this work did not demonstrate the potential of the donor system as a future quantum memory. Here, we show both statistics for single photon emission, as well as the presence of a three-level optical Λ-system through magnetospectroscopy experiments. This introduces F:ZnSe as a valid candidate for use as a scalable qubit with an optical interface.~ 23 meV TES I 2 FE-LH FE-HH c) pump D 0 X D 0 1s 2s,2p I 2 2s-TES 21 meV b) Zn 0.92 Mg 0.08 Se Zn 0.92 M...

Here we demonstrate optical pumping of a single electron within a semiconductor nanostructure comprised of a single fluorine donor located within a ZnSe/ZnMgSe quantum well. Experiments were performed to detect optical pumping behavior by observing single photons emitted from the nanostructure when the electron changes spin state. These results demonstrate initialization and read-out of the electron spin qubit and open the door for coherent optical manipulation of a spin by taking advantage of an unconventional nanostructure.

Quantum communication systems based on nanoscale semiconductor devices is challenged by inhomogeneities from device to device. We address this challenge using ZnMgSe/ZnSe quantum-well nanostructures with local laser-based heating to tune the emission of single impurity-bound exciton emitters in two separate devices. The matched emission in combination with photon bunching enables quantum interference from the devices and allows the postselection of polarization-entangled single photons. The ability to entangle single photons emitted from nanometer-sized sources separated by macroscopic distances provides an essential step for a solid-state realization of a large-scale quantum optical network. This paves the way toward measurement-based entanglement generation between remote electron spins localized at macroscopically separated fluorine impurities.

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