The uncontrolled interaction of a quantum system with its environment is detrimental for quantum coherence. For quantum bits in the solid state, decoherence from thermal vibrations of the surrounding lattice can typically only be suppressed by lowering the temperature of operation. Here, we use a nano-electro-mechanical system to mitigate the effect of thermal phonons on a spin qubit – the silicon-vacancy colour centre in diamond – without changing the system temperature. By controlling the strain environment of the colour centre, we tune its electronic levels to probe, control, and eventually suppress the interaction of its spin with the thermal bath. Strain control provides both large tunability of the optical transitions and significantly improved spin coherence. Finally, our findings indicate the possibility to achieve strong coupling between the silicon-vacancy spin and single phonons, which can lead to the realisation of phonon-mediated quantum gates and nonlinear quantum phononics.

Quantum entanglement between distant qubits is an important feature of quantum networks. Distribution of entanglement over long distances can be enabled through coherently interfacing qubit pairs via photonic channels. Here, we report the realization of optically generated quantum entanglement between electron spin qubits confined in two distant semiconductor quantum dots. The protocol relies on spin-photon entanglement in the trionic Λ system and quantum erasure of the Raman-photon path information. The measurement of a single Raman photon is used to project the spin qubits into a joint quantum state with an interferometrically stabilized and tunable relative phase. We report an average Bell-state fidelity for jψ ðþÞ i and jψ ð−Þ i states of 61.6 AE 2.3% and a record-high entanglement generation rate of 7.3 kHz between distant qubits. DOI: 10.1103/PhysRevLett.119.010503 The refutation of local realism in favor of a nonlocal quantum theory [1,2] has been supported by a number of decisive experiments using entangled pairs of photons [3,4], atoms [5,6], and solid-state systems [7,8]. While photonic links are essential to close loopholes in Bell tests by removing the requirement of spatial proximity for entanglement creation, they also permit flexible arrangements in which distant systems with a spin-photon interface can be entangled. The emergence of entanglement as a central resource in quantum sensing, communication, and computation [9] benefits from this flexibility, where matter qubits coherently coupled to well-defined optical modes provide the elementary constituents of a distributed quantum network [10]. Accordingly, the creation of entangled states between distant qubits has received intense experimental attention in a number of physical systems [6,[11][12][13][14][15][16]. The operation rate of any quantum network would ultimately depend upon the strength of the light-matter coupling between stationary and flying qubits. In this regard, indium-gallium-arsenide (InGaAs) quantum dots (QDs) feature a particularly high oscillator strength of the spin-photon interface, with the potential for high rates of entanglement distribution [17]. Matter qubits can be realized using confined electrons [18], heavy holes [19], or dark excitons [20] in these systems. While quantum correlations have been observed between distant heavy hole spins [15], it is the electron that offers the longest coherence time in this system to date [21][22][23].In this Letter, we present optical generation of nonlocal quantum-entangled states between two distant nodes formed by electron spins confined in separate QDs. Through a single-photon state projection protocol [24] and the bright narrow-linewidth emission available from QDs [25], we realize an entanglement generation rate of 7.3 kHz, the highest rate to date. Further, with full control over the singlephoton interference, we create remote entangled states with an arbitrary phase. Prior to this point, phase control of the generated entangled state had only been demonstrated for atomic...

The electronic energy levels and optical transitions of a semiconductor quantum dot are subject to dynamics within the solid-state environment. In particular, fluctuating electric fields due to nearby charge traps or other quantum dots shift the transition frequencies via the Stark effect. The environment dynamics are mapped directly onto the fluorescence under resonant excitation and diminish the prospects of quantum dots as sources of indistinguishable photons in optical quantum computing. Here, we present an analysis of resonance fluorescence fluctuations based on photon counting statistics which captures the underlying time-averaged electric field fluctuations of the local environment. The measurement protocol avoids dynamic feedback on the electric environment and the dynamics of the quantum dot's nuclear spin bath by virtue of its resonant nature and by keeping experimental control parameters such as excitation frequency and external fields constant throughout. The method introduced here is experimentally undemanding.

Explainability in machine learning is crucial for iterative model development, compliance with regulation, and providing operational nuance to model predictions. Shapley values provide a general framework for explainability by attributing a model's output prediction to its input features in a mathematically principled and model-agnostic way. However, practical implementations of the Shapley framework make an untenable assumption: that the model's input features are uncorrelated. In this work, we articulate the dangers of this assumption and introduce two solutions for computing Shapley explanations that respect the data manifold. One solution, based on generative modelling, provides flexible access to on-manifold data imputations, while the other directly learns the Shapley value function in a supervised way, providing performance and stability at the cost of flexibility. While the commonly used "off-manifold" Shapley values can (i) break symmetries in the data, (ii) give rise to misleading wrong-sign explanations, and (iii) lead to uninterpretable explanations in high-dimensional data, our approach to on-manifold explainability demonstrably overcomes each of these problems.

We present a magneto-photoluminescence study on neutral and charged excitons confined to InAs/GaAs quantum dots. Our investigation relies on a confocal microscope that allows arbitrary tuning of the angle between the applied magnetic field and the sample growth axis. First, from experiments on neutral excitons and trions, we extract the in-plane and on-axis components of the Landé tensor for electrons and holes in the s-shell. Then, based on the doubly negatively charged exciton magneto-photoluminescence we show that the p-electron wave function spreads significantly into the GaAs barriers. We also demonstrate that the p-electron g-factor depends on the presence of a hole in the s-shell. The magnetic field dependence of triply negatively charged excitons photoluminescence exhibits several anticrossings, as a result of coupling between the quantum dot electronic states and the wetting layer. Finally, we discuss how the system evolves from a KondoAnderson exciton description to the artificial atom model when the orientation of the magnetic field goes from Faraday to Voigt geometry.