myserverLLM-filtered feed (spin_qubits)enFri, 10 Apr 2026 03:47:46 +0000https://arxiv.org/abs/2604.06766reply.relevance=7 reply.impact=8 Artificial atoms based on color centers in silicon (SiCCs) have recently emerged as promising candidates for highly integrable and scalable key components in photonic quantum technology, including telecom single-photon sources and spin memory devices. A novel all-epitaxial fabrication technique for SiCCs, based on ultra-low-temperature (ULT) molecular beam epitaxy (MBE), addresses limitations of conventional fabrication via ion implantation, such as vertical ion straggle and collateral crystal lattice damage. This method solely relies on self-assembly of SiCCs during kinetically-limited growth of (carbon-doped) Si(:C) at ULTs <~350{\deg}C. The latter requires an extraordinary pristine growth environment to prevent unintended defect formation caused by the incorporation of impurities from the background vapor; however, so far, no study has specifically addressed how exactly the vacuum conditions during epitaxy influence SiCC formation, their optical properties, and the quality of the surrounding crystal matrix. Here, we investigate the impact of the growth pressure and the substrate temperature on the self-assembly and photoluminescence (PL) properties of important SiCCs, such as W, G, G', and T centers. Further, we use PL and Doppler broadening variable energy positron annihilation spectroscopy to emphasize the role of the growth pressure in suppressing the luminescence background, which is crucial for advancing quantum photonics applications.Fri, 10 Apr 2026 03:47:46 +0000https://arxiv.org/abs/2604.06869reply.relevance=7 reply.impact=7 Secure communications with quantum key distribution over fiber-optic links is one of the few recognized applications of quantum physics at the level of individual quanta -- single C-band photons. Currently, the widely used sources of such photons are highly attenuated laser pulses, featured by a low probability of single photon occurrence. Here, we present an efficient source with an InAs/GaAs quantum dot on a metamorphic buffer layer inside a micropillar-shaped microcavity. The key innovation is the use of different semiconductor and dielectric materials to form the lower (GaAs/AlGaAs) and upper (Si/SiO$_2$) Bragg reflectors. Compatibility of these materials in a monolithic source is achieved by depositing a small amount of Si/SiO$_2$ pairs on an incomplete micropillar made from a coherent heterostructure grown by molecular beam epitaxy. This design enables resonant excitation with $\pi$-pulses and generation of polarized photons with a record-breaking end-to-end efficiency of 11%.Fri, 10 Apr 2026 03:47:46 +0000https://arxiv.org/abs/2604.06944reply.relevance=8 reply.impact=7 Transport through correlated nanoscale systems underpins the operation of quantum-dot and molecular-scale devices, yet accurate simulations of large open quantum systems remain computationally challenging as system size increases. Tensor-network methods offer a promising route past this scaling barrier by efficiently compressing quantum states. Here we extend a tensor-based solver with a jump-counting estimator that enables direct computation of steady-state electron currents from lead-induced tunneling events. We benchmark the resulting currents against the state-of-the-art master-equation solver QmeQ across a range of lead-dot and inter-dot coupling parameters and find quantitative agreement in the tractable regime. Compared with classical approaches, TJM reduces memory requirements and wall-clock time by orders of magnitude, enabling simulations of interacting quantum-dot arrays far beyond the range accessible to density-matrix-based transport solvers and systematic studies of size-dependent nonequilibrium transport in larger arrays. Our approach allow us to model quantum transport in an array of up to fifty (50) quantum dots.Fri, 10 Apr 2026 03:47:46 +0000https://arxiv.org/abs/2604.07074reply.relevance=7 reply.impact=8 We demonstrate complete coherent control of a single spin qubit confined in a self-assembled InAs negatively charged quantum dot subjected to an Oblique magnetic field, and directly compare this regime with the conventional Voigt geometry. In the Oblique-field configuration, the groundstate spin eigenstates are found to be unequal superpositions of the bare electron spin, with their composition tunable via the orientation of the applied field. This tunable spin mixing provides an additional degree of freedom to engineer the spin basis and associated optical couplings in the charged quantum dot system. Although this geometry has a distinct structure with important implications, it provides a regime in which we can fully and coherently control the tailored spin qubit. We observe Rabi oscillations and Ramsey fringes, and demonstrate arbitrary single-qubit rotations, enabling a direct comparison with the Voigt case. Our results establish that spin-qubit control does not necessarily require a pure Voigt geometry and can instead be achieved under Oblique magnetic fields. This relaxes constraints on device and field alignment and offers a versatile route to design and optimize quantum information processing architectures in semiconductor quantum dots.Fri, 10 Apr 2026 03:47:46 +0000https://arxiv.org/abs/2502.15897reply.relevance=7 reply.impact=6 In quantum nanoelectronics devices, the electrostatic energy is the largest energy scale at play and, to a large extend, it determines the charge distribution inside the devices. Here, we introduce the Pure Electrostatic Self consistent Approximation (PESCA) that provides a minimum model that describes how to include a semiconductor in an electrostatic calculation to properly account for both screening and partial depletion due to e.g. field effect. We show how PESCA may be used to reconstruct the charge distribution from the measurement of pinch-off phase diagrams in the gate voltages space. PESCA can also be extended to account for magnetic field and calculate the edge reconstruction in the quantum Hall regime. The validity of PESCA is controlled by a small parameter $\kappa = C_g/C_q$, the ratio of the geometrical capacitance to the quantum capacitance, which is, in many common situations, of the order of 1%, making PESCA a quantitative technique for the calculation of the charge distribution inside devices.Fri, 10 Apr 2026 03:47:46 +0000https://arxiv.org/abs/2602.21364reply.relevance=7 reply.impact=8 In superconductor-semiconductor hybrid structures, superconductivity and spin polarization are competing effects because magnetic fields break Cooper pairs. They can be combined using thin films and in-plane magnetic fields, an approach that enabled the pursuit of Majorana zero modes, Kitaev chains, and Andreev spin qubits (ASQs), but remains challenging for materials with small in-plane g-factors. Here we show that granular aluminum (grAl), composed of nanometer-scale aluminum grains embedded in an amorphous oxide matrix, can overcome this limitation. By depositing grAl on Ge/SiGe heterostructures, we induce a hard superconducting gap with BCS peaks at 305 $\mu$eV and magnetic-field resilience for both the in-plane and out-of-plane directions, allowing Zeeman splitting of Yu-Shiba-Rusinov (YSR) states beyond 50 $\mu$eV (12 GHz). Leveraging this robustness, we reveal signatures of hole physics and demonstrate g-tensor tunability.Fri, 10 Apr 2026 03:47:46 +0000https://arxiv.org/abs/2603.11635reply.relevance=7 reply.impact=8 Valley degrees of freedom are a promising resource for solid-state quantum information. However, traditional architectures rely on engineered valley energy splitting in semiconductors, an approach incompatible with the gapless, degenerate valleys of Dirac and Weyl materials. Here, we propose a single-qubit valley phase gate based on the coherent transport of tilted Dirac/Weyl fermions. Instead of relying on energy splitting, our scheme exploits the opposing geometric tilt of momentum-separated Dirac cones. By routing wave-packets through a shaped electrostatic barrier, the valley-dependent tilt induces differential spatial drift and dwell times, accumulating a continuously tunable relative dynamical phase. Time-dependent transport simulations demonstrate ultrafast, electrically tunable $R_z$ rotations (including $\pi/4$, $\pi/2$, and $\pi$ targets) operating on equal-energy valleys, with strong mode preservation in the low electrostatic potential regime. Furthermore, we identify mode distortion and orbital mismatch, rather than phase randomization, as the primary mechanism that limits ideal unitary behavior at higher barrier heights. This work establishes a transport-based route to coherent valley-qubit manipulation driven purely by relativistic transport dynamics.Fri, 10 Apr 2026 03:47:46 +0000