arXiv subjects

A. Danilov

Publications and source records attributed to A. Danilov.

7 recordsLinked to original sources

arXiv2025

An ultra-compact deterministic source of maximally entangled photon pairs

We present an ultra-compact source of maximally entangled on-demand photon pairs. Our results are based on coupling of single GaAs quantum dots that are embedded in monolithic micro-lenses to a single-mode fiber with directly attached to 3D-printed micro-optics (NA of 0.6) inside a cryogenic environment. This approach, which is geared towards future integration into industrial environments, yields state-of-the-art entangled photon pair creation performance while retaining flexibility and adjustability required for long-term operation of such a device - all while dramatically reducing the overall system footprint. We demonstrate near diffraction-limited performance and hyperspectral imaging utilizing a 3D-printed micro-objective with a full width at half maximum resolution limit of 604(16) nm when operating the system at a cryogenic temperature of 3.8 K. Furthermore, we prove that this system can be used to achieve single photon emission rates of 392(20) kHz at a 76 MHz pump rate and purities of 99.2(5) % using two-photon resonant excitation. Utilizing the exciton-biexciton emission cascade available in GaAs quantum dots under resonant excitation, near maximally entangled photon pairs with peak entanglement negatives 2n of 0.96(2) in a 4 ps time window, and 0.81(1) when averaged over one exciton lifetime, are demonstrated.

quant-ph↗

arXiv2024

Effect of antiprotons on hydrogen-like ions in external magnetic fields

In the present work, quasi-molecular compounds consisting of one antiproton ($\bar{p}$) and one hydrogen-like ion are investigated: $\mathrm{He}^{+} - \bar{p}$, $\mathrm{Li}^{2+} - \bar{p}$, $\mathrm{C}^{5+} - \bar{p}$, $\mathrm{S}^{15+} - \bar{p}$, $\mathrm{Kr}^{35+} - \bar{p}$, $\mathrm{Ho}^{66+} - \bar{p}$, $\mathrm{Re}^{74+} - \bar{p}$, $\mathrm{U}^{91+} - \bar{p}$. For the calculations, the Dirac equation with two-center potential is solved numerically using the dual-kinetically balanced finite-basis-set method adapted to systems with axial symmetry (A-DKB). Adiabatic potential curves are constructed for the ground state of the above quasi-molecular compounds in the framework of the A-DKB approach. Calculations were also performed for the case of an external magnetic field (the field is taken into account non-perturbatively). Zeeman shifts of the quasi-molecular terms are obtained for a homogeneous magnetic field with a strength of the laboratory order (up to 100 Tesla) directed along the axis of the molecule.

physics.atom-ph↗

arXiv2023

Light one-electron quasi-molecular ions within the finite-basis-set method for the two-center Dirac equation

The electronic spectra of light one-electron quasi-molecular compounds H-H$^+$, He$^+$-He$^2+$ and He$^+$-H$^+$ are analyzed. To this end, the two-center Dirac equation is solved by the dual-kinetically balanced finite-basis-set method for axially symmetric systems termed as A-DKB. This method allows a complete relativistic consideration of these systems at fixed internuclear distances. A comparison of the obtained results with the nonrelativistic and relativistic calculations presented in the literature is performed. The advantages and disadvantages of the approach are discussed in details.

physics.atom-ph↗

arXiv2023

Reflection-enhanced gain in traveling-wave parametric amplifiers

The operating principle of traveling-wave parametric amplifiers is typically understood in terms of the standard coupled mode theory, which describes the evolution of forward propagating waves without any reflections, i.e. for perfect impedance matching. However, in practice, superconducting microwave amplifiers are unmatched nonlinear finite-length devices, where the reflecting waves undergo complex parametric processes, not described by the standard coupled mode theory. Here, we present an analytical solution for the TWPA gain, which includes the interaction of reflected waves. These reflections result in corrections to the well-known results of the standard coupled mode theory, which are obtained for both 3-wave and 4-wave mixing processes. Due to these reflections, gain is enhanced and unwanted nonlinear phase modulations are suppressed. Predictions of the model are experimentally demonstrated on two types of unmatched TWPA, based on coplanar waveguides with a central wire consisting of i) a high kinetic inductance superconductor, and ii) an array of 2000 Josephson junctions.

cond-mat.mtrl-sci↗

arXiv2023

Topological Darkness: How to Design a Metamaterial for Optical Biosensing with Virtually Unlimited Sensitivity

Due to the absence of labels and fast analyses, optical biosensors promise major advances in biomedical diagnostics, security, environmental and food safety applications. However, sensitivity of the most advanced plasmonic biosensor implementations has a fundamental limitation caused by losses in the system and or geometry of biochips. Here, we report a scissor effect in topologically dark metamaterials which is capable of providing virtually unlimited bona fide sensitivity to biosensing thus solving the bottleneck sensitivity limitation problem. We explain how the scissor effect can be realized via a proper design of topologically dark metamaterials and describe strategies for their fabrication. To validate the applicability of this effect in biosensing, we demonstrate the detection of folic acid (vitamin important for human health) in the wide 3-log linear dynamic range with the limit of detection of 0.125 nM, which is orders of magnitude better than previously reported for all optical counterparts. Our work opens possibilities for designing and realising plasmonic, semiconductor and dielectric metamaterials with ultra-sensitivity to binding events.

physics.optics↗

arXiv2020

Fast tunable high Q-factor superconducting microwave resonators

We present fast tunable superconducting microwave resonators fabricated from planar NbN on a sapphire substrate. The $3λ/4$ wavelength resonators are tuning fork shaped and tuned by passing a dc current which controls the kinetic inductance of the tuning fork prongs. The $λ/4$ section from the open end operates as an integrated impedance converter which creates a nearly perfect short for microwave currents at the dc terminal coupling points, thus preventing microwave energy leakage through the dc lines. We measure an internal quality factor $Q_{\rm int}>10{^{5}}$ over the entire tuning range. We demonstrate a tuning range of $> 3\%$ and tuning response times as short as 20 ns for the maximum achievable detuning. Due to the quasi-fractal design, the resonators are resilient to magnetic fields of up to 0.5 T.

physics.app-ph↗

arXiv2019

Towards quantum-limited coherent detection of terahertz waves in charge-neutral graphene

Spectacular advances in heterodyne astronomy with both the Herschel Space Observatory and Stratospheric Observatory for Far Infrared Astronomy (SOFIA) have been largely due to breakthroughs in detector technology. In order to exploit the full capacity of future THz telescope space missions (e.g. Origins Space Telescope), new concepts of THz coherent receivers are needed, providing larger bandwidths and imaging capabilities with multi-pixel focal plane heterodyne arrays. Here we show that graphene, uniformly doped to the Dirac point, enables highly sensitive and wideband coherent detection of THz signals. With material resistance dominated by quantum localization, and thermal relaxation governed by electron diffusion, proof-of-concept graphene bolometers demonstrate a gain bandwidth of 8 GHz and a mixer noise temperature of 475 K, limited by residual thermal background in our setup. An optimized device will result in a mixer noise temperature as low as 36 K, with the gain bandwidth exceeding 20 GHz, and a Local Oscillator power lower than 100 pW. In conjunction with the emerging quantum-limited amplifiers at the intermediate frequency, our approach promises quantum-limited sensing in the THz domain, potentially surpassing superconducting technologies, particularly for large heterodyne arrays.

cond-mat.mes-hall↗