Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Simulators for photonic quantum information processing (PQIP) experiments are essentially different with currently available quantum-circuit simulators. In PQIP experiments, photons are usually encoded by multiple degrees of freedom, some of which are multi-level or even infinite-level. Moreover, the evolution of indistinguishable photons cannot be described elegantly by the model used in quantum-circuit simulators. A simulator focusing on PQIP experiments is urgently needed, as it plays an important role in PQIP experiments designing and verification. We developed PhotoniQLAB, an object-oriented framework designed for simulating PQIP experiments, which provides a virtual-lab user experience. The core simulation unit is a computer algebraic system based on the second quantization method. PhotoniQLAB only requires users to enter the structure information of a target PQIP experiment to conduct a simulation, as it can understand the topological structure by itself. The mathematical foundation and technical details of PhotoniQLAB are discussed in the paper. The performance of PhotoniQLAB, which is analyzed and used to simulate several experimental schemes in this paper, has been shown to be efficient enough for near-term PQIP experiments. PhotoniQLAB shows its flexibility and universality, through simulating more than 60 existing PQIP experiments in published papers. We believe that PhotoniQLAB will become a fundamental PQIP software infrastructure facilitating the analyses and designs of PQIP experiments.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Numerous astrophysical and cosmological observations are best explained by the existence of dark matter, a mass density which interacts only very weakly with visible, baryonic matter. Searching for the extremely weak signals produced by this dark matter strongly motivate the development of new, ultra-sensitive detector technologies. Paradigmatic advances in the control and readout of massive mechanical systems, in both the classical and quantum regimes, have enabled unprecedented levels of sensitivity. In this white paper, we outline recent ideas in the potential use of a range of solid-state mechanical sensing technologies to aid in the search for dark matter in a number of energy scales and with a variety of coupling mechanisms.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Laser-controlled entanglement between atomic qubits (‘spins’) and collective motion in trapped ion Coulomb crystals requires conditional momentum transfer from the laser. Since the spin-dependent force is derived from a spatial gradient in the spin–light interaction, this force is typically longitudinal—parallel and proportional to the average laser <jats:italic>k</jats:italic>-vector (or two beams’ <jats:italic>k</jats:italic>-vector difference), which constrains both the direction and relative magnitude of the accessible spin–motion coupling. Here, we show how momentum can also be transferred perpendicular to a single laser beam due to the gradient in its transverse profile. By controlling the transverse gradient at the position of the ion through beam shaping, the relative strength of the sidebands and carrier can be tuned to optimize the desired interaction and suppress undesired, off-resonant effects that can degrade gate fidelity. We also discuss how this effect may already be playing an unappreciated role in recent experiments.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In the noisy intermediate-scale quantum (NISQ) era, solving the electronic structure problem from chemistry is considered as the ‘killer application’ for near-term quantum devices. In spite of the success of variational hybrid quantum/classical algorithms in providing accurate energy profiles for small molecules, careful considerations are still required for the description of complicated features of potential energy surfaces. Because the current quantum resources are very limited, it is common to focus on a restricted part of the Hilbert space (determined by the set of active orbitals). While physically motivated, this approximation can severely impact the description of these complicated features. A perfect example is that of conical intersections (i.e. a singular point of degeneracy between electronic states), which are of primary importance to understand many prominent reactions. Designing active spaces so that the improved accuracy from a quantum computer is not rendered useless is key to finding useful applications of these promising devices within the field of chemistry. To answer this issue, we introduce a NISQ-friendly method called ‘state-averaged orbital-optimized variational quantum eigensolver’ which combines two algorithms: (1) a state-averaged orbital-optimizer, and (2) a state-averaged VQE. To demonstrate the success of the method, we classically simulate it on a minimal Schiff base model (namely the formaldimine molecule CH<jats:sub>2</jats:sub>NH) relevant also for the photoisomerization in rhodopsin—a crucial step in the process of vision mediated by the presence of a conical intersection. We show that merging both algorithms fulfil the necessary condition to describe the molecule’s conical intersection, i.e. the ability to treat degenerate (or quasi-degenerate) states on the same footing.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a scheme to entangle the vibrational phonon modes of two massive ferromagnetic spheres in a dual-cavity magnomechanical system. In each cavity, a microwave cavity mode couples to a magnon mode (spin wave) via the magnetic dipole interaction, and the latter further couples to a deformation phonon mode of the ferromagnetic sphere via a nonlinear magnetostrictive interaction. We show that by directly driving the magnon mode with a red-detuned microwave field to activate the magnomechanical anti-Stokes process a cavity–magnon–phonon state-swap interaction can be realized. Therefore, if the two cavities are further driven by a two-mode squeezed vacuum field, the quantum correlation of the driving fields is successively transferred to the two magnon modes and subsequently to the two phonon modes, i.e., the two ferromagnetic spheres become remotely entangled. Our work demonstrates that cavity magnomechanical systems allow to prepare quantum entangled states at a more massive scale than currently possible with other schemes.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A ferromagnetic gyroscope (FG) is a ferromagnet whose angular momentum is dominated by electron spin polarization and that will process under the action of an external torque, such as that due to a magnetic field. Here we model and analyze FG dynamics and sensitivity, focusing on practical schemes for experimental realization. In the case of a freely floating FG, we model the transition from dynamics dominated by libration in relatively high externally applied magnetic fields, to those dominated by precession at relatively low applied fields. Measurement of the libration frequency enables <jats:italic>in situ</jats:italic> determination of the magnetic field and a technique to reduce the field below the threshold for which precession dominates the FG dynamics. We note that evidence of gyroscopic behavior is present even at magnetic fields much larger than the threshold field below which precession dominates. We also model the dynamics of an FG levitated above a type-I superconductor via the Meissner effect, and find that for FGs with dimensions larger than about 100 nm the observed precession frequency is reduced compared to that of a freely floating FG. This is due to an effect akin to negative feedback that arises from the distortion of the field from the FG by the superconductor. Finally we assess the sensitivity of an FG levitated above a type-I superconductor to exotic spin-dependent interactions under practical experimental conditions, demonstrating the potential of FGs for tests of fundamental physics.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The control of large-scale quantum information processors based on arrays of trapped ions requires a means to route and focus multiple laser beams to each of many trapping sites in parallel. Here, we combine arrays of fibres, 3D laser-written waveguides and diffractive microlenses to demonstrate the principle of a micro-optic interconnect suited to this task. The module is intended for use with an ion microtrap of 3D electrode geometry. It guides ten independent laser beams with unique trajectories to illuminate a pair of spatially separated target points. Three blue and two infrared beams converge to overlap precisely at each desired position. Typical relative crosstalk intensities in the blue are 3.6 × 10<jats:sup>−3</jats:sup> and the average insertion loss across all channels is 8 dB. The module occupies ∼10<jats:sup>4</jats:sup> times less volume than a conventional bulk-optic equivalent and is suited to different ion species.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We describe a project that brings together researchers from atomic physics, nuclear physics and sub-atomic particle physics, to develop a high-precision laboratory-scale experiment able to search for very weakly coupled sterile neutrinos in the mass range extending from 5–10 keV/<jats:italic>c</jats:italic> <jats:sup>2</jats:sup> to several 100 keV/<jats:italic>c</jats:italic> <jats:sup>2</jats:sup>. Observed neutrino flavor eigenstates are known to be quantum mixtures of at least three sub-eV/<jats:italic>c</jats:italic> <jats:sup>2</jats:sup> mass eigenstates. There is a strong theoretical belief that there may exist further neutrino mass eigenstates at higher mass levels, and which, if in the keV/<jats:italic>c</jats:italic> <jats:sup>2</jats:sup> mass range, might form all or part of the galactic dark matter. This has led to many searches for anomalous events in both astrophysical and particle physics experiments, and searches for distortions in beta decay spectra. The present experiment will utilize <jats:italic>K</jats:italic>-capture events in a population of <jats:sup>131</jats:sup>Cs atoms suspended in vacuum by a magneto-optical trap (MOT). Using AMO and nuclear physics techniques, individual events will be fully reconstructed kinematically. Normally each event would be consistent with an emitted neutrino mass close to zero, but the existence of a sterile neutrino of keV/<jats:italic>c</jats:italic> <jats:sup>2</jats:sup> mass that mixes with the electron type neutrino produced in the decay would result in a separated population of events with non-zero reconstructed missing mass (up to the <jats:italic>Q</jats:italic> = 352 keV available energy of the reaction). Detailed calculations and simulations of all significant background processes have been made, in particular for scattering in the source itself, radiative <jats:italic>K</jats:italic>-capture, local radioactivity, cosmic ray muons, and knock-out of electrons by x-rays. A phase 1 of the experiment, under construction with funding from the W M Keck Foundation, has the potential to reach sterile neutrino mixing angles down to sin<jats:sup>2</jats:sup>  <jats:italic>θ</jats:italic> ∼ 10<jats:sup>−4</jats:sup>. With further upgrades this technique could be progressively improved to eventually reach much lower coupling levels ∼10<jats:sup>−10</jats:sup>, in particular reaching the level needed to be consistent with galactic dark matter below the astrophysical x-ray limits.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Variational quantum algorithms are currently the most promising class of algorithms for deployment on near-term quantum computers. In contrast to classical algorithms, there are almost no standardized methods in quantum algorithmic development yet, and the field continues to evolve rapidly. As in classical computing, heuristics play a crucial role in the development of new quantum algorithms, resulting in a high demand for flexible and reliable ways to implement, test, and share new ideas. Inspired by this demand, we introduce tequila, a development package for quantum algorithms in python, designed for fast and flexible implementation, prototyping and deployment of novel quantum algorithms in electronic structure and other fields. tequila operates with abstract expectation values which can be combined, transformed, differentiated, and optimized. On evaluation, the abstract data structures are compiled to run on state of the art quantum simulators or interfaces.</jats:p>