A Spin–Photon Interface Using Charge-Tunable Quantum Dots Strongly Coupled to a Cavity

Abstract

Charged quantum dots containing an electron or hole spin are bright solid-state qubits suitable for quantum networks and distributed quantum computing. Incorporating such quantum dot spin into a photonic crystal cavity creates a strong spin-photon interface, in which the spin can control a photon by modulating the cavity reflection coefficient. However, previous demonstrations of such spin-photon interfaces have relied on quantum dots that are charged randomly by nearby impurities, leading to instability in the charge state, which causes poor contrast in the cavity reflectivity. Here we demonstrate a strong spin-photon interface using a quantum dot that is charged deterministically with a diode structure. By incorporating this actively charged quantum dot in a photonic crystal cavity, we achieve strong coupling between the cavity mode and the negatively charged state of the dot. Furthermore, by initializing the spin through optical pumping, we show strong spin-dependent modulation of the cavity reflectivity, corresponding to a cooperativity of 12. This spin-dependent reflectivity is important for mediating entanglement between spins using photons, as well as generating strong photon-photon interactions for applications in quantum networking and distributed quantum computing.Keyword: quantum dots, single electron spin, strong light-matter interaction, cavity quantum electrodynamics MainCharged epitaxially-grown Ⅲ-Ⅳ quantum dots that contain an electron or hole spin 1,2 have emerged as a promising solid-state qubit system. They exhibit a high radiative efficiency, 3 which is important for generating single or entangled photons of high brightness. In addition, they support fast all-optical coherent spin rotations on picosecond timescales, 4-6 necessary for high-speed quantum network and quantum information processing. Coupling such charged quantum dots to photonic crystal cavities enables strong spin-photon interfaces, 7 which are essential for solid-state quantum networks 8-10 and the generation of strong photon-photon interactions. [11][12][13] These applications require the spin-state of the quantum dot to modulate the cavity reflectivity, allowing the spin to control the state of the reflected photons (e.g., polarization and frequency).Several studies have demonstrated such strong spin-photon interfaces between the electron spin of a charged quantum dot and cavity, 14-17 enabling optical nonlinearities such as Kerr rotations 16,17 and single-photon transistors. 15 These studies have relied on probabilistically charged quantum AUTHOR INFORMATIONCorresponding Author

Room-temperature electron spin polarization exceeding 90% in an opto-spintronic semiconductor nanostructure via remote spin filtering

“…There has also been an enormous push for semiconductor spintronics during the past two decades [1][2][3][4] , with the aim to capitalize the past and current success of charge-based semiconductor technology and to make its spin counterpart the backbone of future spintronics, just like semiconductors have done in today's electronics/photonics. An exclusive advantage of semiconductor spintronics is its potential to interface with photonic devices that allows exchange of spin quantum information via photons, leading to opto-spintronic devices serving as spin-photon interfaces essential for inter-connects and data communications among and between classical and quantum information nodes and systems [10][11][12] .…”

Quantum repeaters based on individual electron spins and nuclear-spin-ensemble memories in quantum dots

“…Additionally, experimental demonstrations have shown that QDs are promising on-demand single-photon sources with high single-photon purity and indistinguishability [64][65][66]. Implementation of these gates through the use of other QD-cavity single-photon sources represents a promising route towards scalable, onchip quantum logic [67][68][69][70].…”

Optical transparency induced by a largely Purcell-enhanced quantum dot in a polarization-degenerate cavity

“…Here, we fabricate bullseye antennas with nearly degenerate polarization modes to generate a large Purcell enhancement of quantum dots embedded in a charge tunable device, namely a p-i-n-i-n diode [31,32]. By leveraging the low charge noise associated with the diode, we measure spontaneous emission lifetimes of quantum dots as short as ≈ 80 ps (a Purcell enhancement of ≈ 15), which are close to the state-of-the-art optical lifetimes measured on quantum dots coupled to micropillars [3,4,7].…”

“…While such partial etching improves the collection efficiency of photons scattered from the sample, it reduces the quality factor of the bullseye antenna [25], thereby providing a smaller Purcell enhancement compared to the ones observed by us after etching the sacrificial layer. The second factor that contributes to the enhanced optical emission rate is the deterministic charge capabilities provided by the p-i-n-in diode, which result in a reduction of the charge noise in the antenna's environment [31,32]. This low charge noise reduces the effects of spectral wandering of the antenna that may degrade the Purcell enhancement of the emission of the quantum dots coupled to it.…”