arXiv subjects

Pavel A. Bushev

Publications and source records attributed to Pavel A. Bushev.

5 recordsLinked to original sources

arXiv2026

Highly crystalline superconducting TiN resonators grown on thermally reconstructed sapphire

High quality crystalline growth of a thin film on sapphire requires sufficient substrate preparation, often achieved via the use of aggressive chemical cleaning. Direct thermal reconstruction of the sapphire substrate via a CO$_2$ laser beam may allow for an alternative way to prepare the substrate for epitaxy without the use of any chemical processing. Within this work, we demonstrate that thermal annealing of sapphire into its ($\sqrt{31}$$\times$$\sqrt{31}$)$R$$\pm$9° reconstruction is a valid alternative preparation technique for sapphire substrates. TiN films grown via plasma-assisted molecular beam epitaxy upon these substrates exhibit greater crystallinity than those grown on chemically cleaned sapphire substrates. Superconducting resonators fabricated from these films exhibit similar performance, with many possessing internal quality factors at single photon levels greater than 10$^6$ for both substrate preparation methods.

cond-mat.supr-con↗

arXiv2026

Contactless terahertz mapping of wafer-scale superconducting NbTiN thin films

For large-scale superconducting quantum technology, e.g. quantum computing, the homogeneity of wafer-scale superconducting thin films is vital for consistent performance of the fabricated devices. Terahertz (THz) spectroscopy as a contactless and non-destructive measurement technique is a powerful tool to characterize the superconducting films. In this work, a set of niobium titanium nitride (NbTiN) thin films on 4-inch and 6-inch silicon wafers, grown via plasma-enhanced magnetron sputtering, are investigated via THz spectroscopy: full wafers are mapped at room temperatures and exemplary segments are characterized at cryogenic temperatures. The deviations in observed sheet resistance depend on the used deposition device and the film thickness. While the deviations in superconducting sheet kinetic inductance match those of the normal-state sheet resistance, the critical temperature and energy gap exhibit little variation. This THz mapping technique demonstrates the feasibility of evaluating wafer-scale superconducting thin films before lithography, facilitating preparation of the thin films for reproducible device fabrication.

cond-mat.supr-con↗

arXiv2025

Broadband electron paramagnetic resonance spectroscopy of $^{167}$Er:$^{7}$LiYF$_4$ at mK temperatures

Rare-earth spin ensembles are a promising platform for microwave quantum memory applications due to their hyperfine transitions, which can exhibit exceptionally long coherence times when using an operation point with zero first-order Zeeman (ZEFOZ) shift. In this work, we use broadband electron paramagnetic resonance (EPR) spectroscopy on $^{167}$Er:$^{7}$LiYF$_4$ single crystals at sub-Kelvin temperatures. By fitting the spin Hamiltonian to the zero-field spectrum, we obtain refined parameters of the magnetic field-independent interactions, such as the hyperfine and quadrupole interaction. We also study the influence of the quadrupole interaction on the hyperfine splitting in the zero and low magnetic field range by analyzing EPR-spectra between 0 mT and 50 mT. Our findings highlight the broadband EPR spectroscopy approach as a powerful tool for the precise determination of the spin Hamiltonian parameters and for the characterization of hyperfine transitions in terms of their selection rules and linewidth.

quant-ph↗

arXiv2020

Electromagnetically Induced Transparency in a mono-isotopic $^{167}$Er:$^7$LiYF$_4$ crystal below 1 Kelvin

Electromagnetically induced transparency allows for controllable change of absorption properties which can be exploited in a number of applications including optical quantum memory. In this paper, we present a study of the electromagnetically induced transparency in $^{167}$Er:$^6$LiYF$_4$ crystal at low magnetic fields and ultra-low temperatures. Experimental measurement scheme employs optical vector network analysis which provides high precision measurement of amplitude, phase and pulse delay. We found that sub-Kelvin temperatures are the necessary requirement for studying electromagnetically induced transparency in this crystal at low fields. A good agreement between theory and experiment is achieved taking into account the phonon bottleneck effect.

quant-ph↗

arXiv2017

Optical coherence of $^{166}$Er:$^{7}$LiYF$_4$ crystal below 1 Kelvin

We explore spin dynamics of isotopically purified $^{166}$Er:$^{7}$LiYF$_4$ crystal below 1 Kelvin and at weak magnetic fields $<$0.3 T. Crystals grown in our lab demonstrate record-narrow inhomogeneous optical broadening down to 16~MHz. Solid state atomic ensembles with such narrow linewidths are very attractive for the implementation of off-resonant Raman quantum memory and for the interfacing of superconducting quantum circuits and telecom C-band optical photons. Both applications require low magnetic field of $\sim10$ mT. However, at conventional experimental temperatures $T>1.5$ K and time scales of $μ$s, spin coherence of Er:LYF crystal appears only at magnetic fields above 1 Tesla. In the present work, we demonstrate spin coherence of Er:LYF crystals at the field range compatible with ZEFOZ transitions of $^{167}$Er isotope and with working conditions of superconducting quantum circuits.

physics.optics↗