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Noise spectroscopy elucidates the fundamental noise sources in spin systems, which is essential for developing spin qubits with long coherence times for quantum information processing, communication, and sensing. But noise spectroscopy typically relies on microwave coherent spin control to extract the noise spectrum, which becomes infeasible when there are high-frequency noise components stronger than the available microwave power. Here, we demonstrate an alternative all-optical approach to performing noise spectroscopy. Our approach utilises coherent Raman rotations of the spin state with controlled timing and phase to implement Carr-Purcell-Meiboom-Gill (CPMG) pulse sequences. Analysing the spin dynamics under these sequences enables us to extract the noise spectrum of a dense ensemble of nuclear spins interacting with a single spin in a quantum dot, which has thus far only been modelled theoretically. By providing large spectral bandwidths of over 100 MHz, our Raman-based approach could serve as an important tool to study spin dynamics and decoherence mechanisms for a broad range of solid-state spin qubits.

Radiative cascades emit correlated photon pairs, providing a pathway for the generation of entangled photons. The realization of a radiative cascade with impurity atoms in semiconductors, a leading platform for the generation of quantum light, would therefore provide a new avenue for the development of entangled photon pair sources. Here we demonstrate a radiative cascade from the decay of a biexciton at an impurity-atom complex in a ZnSe quantum well. The emitted photons show clear temporal correlations revealing the time--ordering of the cascade. Our result establishes impurity atoms in ZnSe as a potential platform for photonic quantum technologies using radiative cascades., Comment: 5 pages, 4 figures

Defects in wide-bandgap semiconductors are promising qubit candidates for quantum communication and computation. Epitaxially grown II-VI semiconductors are particularly promising host materials due to their direct bandgap and potential for isotopic purification to a spin-zero nuclear background. Here, we show a new type of single photon emitter with potential electron spin qubit based on Cl impurities in ZnSe. We utilize a quantum well to increase the binding energies of donor emission and confirm single photon emission with short radiative lifetimes of 192 ps. Furthermore, we verify that the ground state of the Cl donor complex contains a single electron by observing two-electron satellite emission, leaving the electron in higher orbital states. We also characterize the Zeeman splitting of the exciton transition by performing polarization-resolved magnetic spectroscopy on single emitters. Our results suggest single Cl impurities are suitable as single photon source with potential photonic interface., Comment: 7 pages, 6 figures

We introduce an all-optical approach for noise spectroscopy of solid-state spin qubits, based on Raman control and the Carr-Purcell-Meiboom-Gill pulse sequences, and use it to extract the noise spectra of self-assembled quantum dots.

We present theoretical and experimental investigations of higher order correlations of mechanical motion in the recently demonstrated optical tweezer phonon laser, consisting of a silica nanosphere trapped in vacuum by a tightly focused optical beam [Nat. Photonics 13, 402 (2019)10.1038/s41566-019-0395-5]. The nanoparticle phonon number probability distribution is modeled with the master equation formalism in order to study its evolution across the lasing threshold. Up to fourth-order equal-time correlation functions are then derived from the probability distribution. Subsequently, the master equation is transformed into a nonlinear quantum Langevin equation for the trapped particle’s position. This equation yields the non-equal-time correlations, also up to fourth order. Finally, we present experimental measurements of the phononic correlation functions, which are in good agreement with our theoretical predictions. We also compare the experimental data to existing analytical Ginzburg-Landau theory where we find only a partial match.

The efficient single photon emission capabilities of quantum dot molecules position them as promising platforms for quantum information processing. Furthermore, quantum dot molecules feature a "decoherence-free" subspace that enables spin qubits with long coherence time. To efficiently read out the spin state within this subspace requires optically cycling isolated transitions that originate from a triplet manifold within the quantum dot molecule. We propose and theoretically study a two-stage spin readout protocol within this decoherence-free subspace that allows single-shot readout performance. The process incorporates a microwave $\pi$-pulse and optically cycling the isolated transitions, which induces fluorescence that allows us to identify the initial spin state. This protocol offers enhanced readout fidelity compared to previous schemes that rely on the excitation of transitions that strongly decay to multiple ground states or require long initialization via slow, optically forbidden transitions. By simulating the performance of the protocol, we show that an optimal spin readout fidelity of over 97% and single-shot readout performance are achievable for a photon collection efficiency of just 0.12%. This high readout performance for such realistic photon collection conditions within the decoherence-free subspace expands the potential of quantum dot molecules as building blocks for quantum networks.

We demonstrate single photon emission from donor bound excitons in Cl doped ZnSe quantum wells. The emitters are investigated in cryogenic temperatures, and they showed high binding energies and short lifetimes.

We theoretically describe a levitated Mie particle phonon laser, obtained by coupling the particle oscillations to a whispering gallery mode via laser radiation. We show that ultrasensitive force sensing can be performed using this platform.

Optomechanics is concerned with the use of light to control mechanical objects. As a field, it has been hugely successful in the production of precise and novel sensors, the development of low-dissipation nanomechanical devices, and the manipulation of quantum signals. Micro- and nano-particles levitated in optical fields act as nanoscale oscillators, making them excellent low-dissipation optomechanical objects, with minimal thermal contact to the environment when operating in vacuum. Levitated optomechanics is seen as the most promising route for studying high-mass quantum physics, with the promise of creating macroscopically separated superposition states at masses of $10^6$ amu and above. Optical feedback, both using active monitoring or the passive interaction with an optical cavity, can be used to cool the centre-of-mass of levitated nanoparticles well below 1 mK, paving the way to operation in the quantum regime. In addition, trapped mesoscopic particles are the paradigmatic system for studying nanoscale stochastic processes, and have already demonstrated their utility in state-of-the-art force sensing.

A phonon laser based on the center-of-mass oscillations of a silica nanosphere, levitated in an optical tweezer under vacuum, is proposed and developed. The observed dynamics are shown to result from stimulated emission of phonons.

We report the first observation, to the best of our knowledge, of electron spin transients in single negatively charged nitrogen-vacancy (NV−) centers, contained within optically trapped nanodiamonds, in both atmospheric pressure and low vacuum. It is shown that, after an initial exposure to low vacuum, the trapped nanodiamonds remain at temperatures near room temperature even in low vacuum. Furthermore, the transverse coherence time of the NV− center spin, measured to be T2=101.4 ns, is robust over the range of trapping powers considered in this study.

When left and right circularly polarized beams of light from a pump laser interfere in a nematic liquid crystal doped with azo dye, a polarization twisted nematic (PTN) grating is formed in the sample. The same is not true when linearly polarized light interferes, regardless of the polarization. For circularly polarized light, the easy axis is rotated toward the polarization direction of interfering beams. The irradiance is uniform so there is less contribution to refractive index variations. In the latter case the diffraction grating arises from variation in refractive index. Gratings written with Disperse Orange 3 (DO3) as the dopant disappear after removal of the pump beams, whereas grating written with Methyl Red (MR) as the dopant tend to be semi-permanent.

It has been known for some time (6), that there are at least two distinct factors in frost hardinessA: cell sap concentration or sugar content, and B: physicochemical properties of protoplasm. The first must be in some way associated with enzyme activity, since it results from either a starch-sugar conversion or an accumulation of photosynthate in the form of sugar. The second seems to be dependent on protein hydration. Enzyme activation is in many cases associated with SH, and protein hydration depends on the number of polar groups and therefore perhaps on SH. These facts led to the hypothesis that SH might be quantitatively related to frost hardiness, and to the following investigation of that hypothesis. Although there is no record in the literature of an investigation of the relation of SH to frost hardiness there is one report of a relation to drought resistance (4). Since frost hardiness is usually correlated witlh drought hardiness (6), this might be considered as evidence in favor of a relationship between SH and frost hardiness. Unfortunately, no attempt was inade to measure the drought resistance of the several strains of loblolly pine used other than to accept the order "well established by field experiment". The only attempt to measure desiccation resistance in the laboratory failed to yield any relationship to the field determined resistance. This agrees with Parker (7), who could not detect any better ability of the more drought resistance coniferous species to recover from a low leaf moisture than in the case of the less drought resistant species. There was, however, a greater ability to retain a high moisture content. In other words, the available evidence indicates that the drought resistance involved in the above investigation was avoidance rather than tolerance and therefore unrelated to frost resistance.