arXiv subjects

A. Kononov

Publications and source records attributed to A. Kononov.

At least 19 recordsLinked to original sources

arXiv2026

First Experimental Limit on the Permanent Electric Dipole Moment of the Deuteron

Permanent electric dipole moments (EDMs) provide a sensitive probe of physics beyond the Standard Model and are directly linked to additional sources of CP violation that could explain the matter-antimatter asymmetry of the universe. EDM measurements of charged particles in storage rings rely on detecting a small tilt of the invariant spin axis with respect to the ring plane. In this work, we present the experimental determination of the invariant spin axis of an ensemble of deuterons in the COoler SYnchrotron (COSY), a conventional magnetic storage ring, using a combination of a radio-frequency Wien filter, a superconducting Siberian snake and an electron-cooler solenoid. The measurements reveal tilts of a few milliradians, which are dominated by systematic effects. From the observed tilts, we derive the first experimental limit on the deuteron EDM, $|d^d|< 2.5\cdot10^{-17}\,e\cdot\mathrm{cm} \; (95\%\,\text{ C.L.})$. This result demonstrates the feasibility of using storage rings to search for EDMs of charged stable hadrons and provides a foundation for future dedicated facilities.

nucl-ex↗

arXiv2025

Maintaining a Resonance Condition of an RF Spin Rotator Through a Feedback Loop in a Storage Ring

This paper presents the successful application of a phase-lock feedback system to maintain the resonance condition of a radio frequency (rf) spin rotator (specifically, an rf Wien filter) with respect to a 120 kHz spin precession in the Cooler Synchrotron (COSY) storage ring. Real-time monitoring of the spin precession and the rf Wien filter signal allows the relative phase between the two to be stabilized at an arbitrary setpoint. The feedback system compensates for deviations in the relative phase by adjusting the frequency and/or phase as needed. With this method, a variation in phase relative to the demand phase with a standard deviation of $σ_{Δφ}\approx 0.2\mathrm{rad}$ could be achieved. The system was implemented in two runs aiming at a first direct measurement of the deuteron electric dipole moment in 2018 and 2021. In addition, the difference between a single-bunch beam affected by the spin rotator and a two-bunch system in which only one bunch is exposed to the spin rotator fields is discussed. Both methods have been used during these beam times. The ability to keep the spin precession and the rf fields synchronized is also crucial for future investigations of electric dipole moments of charged particles using storage rings.

physics.acc-ph↗

arXiv2023

Photon-mediated long range coupling of two Andreev level qubits

In a superconducting weak link, the supercurrent is carried by Andreev bound states (ABSs) formed by the phase-coherent reflection of electrons and their time-reversed partners. A single, highly transmissive ABS can serve as an ideal, compact two-level system, due to a potentially large energy difference to the next ABS. While the coherent manipulation of such Andreev levels qubits (ALQs) has been demonstrated, a long-range coupling between two ALQs, necessary for advanced qubit architectures, has not been achieved, yet. Here, we demonstrate a coherent remote coupling between two ALQs, mediated by a microwave photon in a novel superconducting microwave cavity coupler. The latter hosts two modes with different coupling rates to an external port. This allows us to perform fast readout of each qubit using the strongly coupled mode, while the weakly coupled mode is utilized to mediate the coupling between the qubits. When both qubits are tuned into resonance with the latter mode, we find excitation spectra with avoided-crossings, in very good agreement with the Tavis-Cummings model. Based on this model, we identify highly entangled two-qubit states for which the entanglement is mediated over a distance of six millimeters. This work establishes ALQs as compact and scalable solid-state qubits.

cond-mat.mes-hall↗

arXiv2023

Spin decoherence and off-resonance behavior of radiofrequency-driven spin rotations in storage rings

Radiofrequency-driven resonant spin rotators are routinely used as standard instruments in polarization experiments in particle and nuclear physics. Maintaining the continuous exact parametric spin-resonance condition of the equality of the spin rotator and the spin precession frequency during operation constitutes one of the challenges. We present a detailed analytic description of the impact of detuning the exact spin resonance on the vertical and the in-plane precessing components of the polarization. An important part of the formalism presented here is the consideration of experimentally relevant spin-decoherence effects. We discuss applications of the developed formalism to the interpretation of the experimental data on the novel pilot bunch approach to control the spin-resonance condition during the operation of the radiofrequency-driven Wien filter that is used as a spin rotator in the first direct deuteron electric dipole moment measurement at COSY. We emphasize the potential importance of the hitherto unexplored phase of the envelope of the horizontal polarization as an indicator of the stability of the radiofrequency-driven spin rotations in storage rings. The work presented here serves as a satellite publication to the work published concurrently on the proof of principle experiment about the so-called pilot bunch approach that was developed to provide co-magnetometry for the deuteron electric dipole moment experiment at COSY.

physics.acc-ph↗

arXiv2023

Pilot bunch and co-magnetometry of polarized particles stored in a ring

In polarization experiments at storage rings, one of the challenges is to maintain the spin-resonance condition of a radio-frequency spin rotator with the spin-precessions of the orbiting particles. Time-dependent variations of the magnetic fields of ring elements lead to unwanted variations of the spin precession frequency. We report here on a solution to this problem by shielding (or masking) one of the bunches stored in the ring from the high-frequency fields of the spin rotator, so that the masked pilot bunch acts as a co-magnetometer for the other signal bunch, tracking fluctuations in the ring on a time scale of about one second. While the new method was developed primarily for searches of electric dipole moments of charged particles, it may have far-reaching implications for future spin physics facilities, such as the EIC and NICA.

physics.ins-det↗

arXiv2023

First Search for Axion-Like Particles in a Storage Ring Using a Polarized Deuteron Beam

Based on the notion that the local dark-matter field of axions or axion-like particles (ALPs) in our Galaxy induces oscillating couplings to the spins of nucleons and nuclei (via the electric dipole moment of the latter and/or the paramagnetic axion-wind effect), we establish the feasibility of a new method to search for ALPs in storage rings. Based on previous work that allows us to maintain the in-plane polarization of a stored deuteron beam for a few hundred seconds, we performed a first proof-of-principle experiment at the Cooler Synchrotron COSY to scan momenta near 970 MeV/c. This entailed a scan of the spin precession frequency. At resonance between the spin precession frequency of deuterons and the ALP-induced EDM oscillation frequency there will be an accumulation of the polarization component out of the ring plane. Since the axion frequency is unknown, the momentum of the beam and consequently the spin precession frequency were ramped to search for a vertical polarization change that would occur when the resonance is crossed. At COSY, four beam bunches with different polarization directions were used to make sure that no resonance was missed because of the unknown relative phase between the polarization precession and the axion/ALP field. A frequency window of 1.5-kHz width around the spin precession frequency of 121 kHz was scanned. We describe the experimental procedure and a test of the methodology with the help of a radiofrequency Wien filter located on the COSY ring. No ALP resonance was observed. As a consequence an upper limit of the oscillating EDM component of the deuteron as well as its axion coupling constants are provided.

hep-ex↗

arXiv2022

Charge-sensing of a Ge/Si core/shell nanowire double quantum dot using a high-impedance superconducting resonator

Spin qubits in germanium are a promising contender for scalable quantum computers. Reading out of the spin and charge configuration of quantum dots formed in Ge/Si core/shell nanowires is typically performed by measuring the current through the nanowire. Here, we demonstrate a more versatile approach on investigating the charge configuration of these quantum dots. We employ a high-impedance, magnetic-field resilient superconducting resonator based on NbTiN and couple it to a double quantum dot in a Ge/Si nanowire. This allows us to dispersively detect charging effects, even in the regime where the nanowire is fully pinched off and no direct current is present. Furthermore, by increasing the electro-chemical potential far beyond the nanowire pinch-off, we observe indications for depleting the last hole in the quantum dot by using the second quantum dot as a charge sensor. This work opens the door for dispersive readout and future spin-photon coupling in this system.

cond-mat.mes-hall↗

arXiv2020

Beam-based alignment at the Cooler Synchrotron COSY as a prerequisite for an electric dipole moment measurement

The Jülich Electric Dipole moment Investigation (JEDI) collaboration aims at a direct measurement of the Electric Dipole Moment (EDM) of protons and deuterons using a storage ring. The measurement is based on a polarization measurement. In order to reach highest accuracy, one has to know the exact trajectory through the magnets, especially the quadrupoles, to avoid the influence of magnetic fields on the polarization vector. In this paper, the development of a beam-based alignment technique is described that was developed and implemented at the COoler SYnchrotron (COSY) at Forschungszentrum Jülich. Well aligned quadrupoles permit one to absolutely calibrate the Beam Position Monitors (BPMs). The method is based on the fact that a particle beam, which does not pass through the center of a quadrupole, experiences a deflection. The precision reached by the method is approximately 40 micro meter. Some consequences for the design of a new high precision storage ring for EDM mesasurements are discussed.

physics.acc-ph↗

arXiv2018

Multivalued current-phase relationship in a.c. Josephson effect for a three-dimensional Weyl semimetal WTe$_2$

We experimentally study electron transport between two superconducting indium leads, coupled to a single WTe$_2$ crystal, which is a three-dimensional Weyl semimetal. We demonstrate Josephson current in long 5~$μ$m In-WTe$_2$-In junctions, as confirmed by the observation of integer (1,2,3) and fractional (1/3, 1/2, 2/3) Shapiro steps under microwave irradiation. Demonstration of fractional a.c. Josephson effect indicates multivalued character of the current-phase relationship, which we connect with Weyl topological surface states contribution to Josephson current. In contrast to topological insulators and Dirac semimetals, we do not observe $4π$ periodicity in a.c. Josephson effect for WTe$_2$ at different frequencies and power, which might reflect chiral character of the Fermi arc surface states in Weyl semimetal.

cond-mat.mes-hall↗

arXiv2018

Spin wave effects in transport between a ferromagnet and a Weyl semimetal surface

We experimentally investigate spin-polarized transport between a ferromagnetic Ni electrode and a surface of Weyl semimetal, realized in a thick WTe$_2$ single crystal. For highly-transparent Ni-WTe$_2$ planar junctions, we observe non-Ohmic $dV/dI(I)$ behavior with an overall increase of differential resistance $dV/dI$ with current bias, which is accomplished by current-induced switchings. This behavior is inconsistent with trivial interface scattering, but it is well known for spin-polarized transport with magnon emission. Thus, we interpret the experimental results in terms of spin wave excitation in spin textures in the WTe$_2$ topological surface states, which is supported by the obtained magnetic field and temperature $dV/dI(I)$ dependencies.

cond-mat.mes-hall↗

arXiv2018

Signature of Fermi arc surface states in Andreev reflection at the WTe$_2$ Weyl semimetal surface

We experimentally investigate charge transport through the interface between a niobium superconductor and a three-dimensional WTe$_2$ Weyl semimetal. In addition to classical Andreev reflection, we observe sharp non-periodic subgap resistance resonances. From an analysis of their positions, magnetic field and temperature dependencies, we can interpret them as an analog of Tomasch oscillations for transport along the topological surface state across the region of proximity-induced superconductivity at the Nb-WTe$_2$ interface. Observation of distinct geometrical resonances implies a specific transmission direction for carriers, which is a hallmark of the Fermi arc surface states.

cond-mat.mes-hall↗

arXiv2018

Andreev reflection at the edge of a two-dimensional electron system with strong spin-orbit coupling

We experimentally investigate transport properties of a single planar junction between the niobium superconductor and the edge of a two-dimensional electron system in a narrow $In_{0.75}Ga_{0.25}As$ quantum well with strong Rashba-type spin-orbit coupling. We experimentally demonstrate suppression of Andreev reflection at low biases at ultra low temperatures. From the analysis of temperature and magnetic field behavior, we interpret the observed suppression as a result of a spin-orbit coupling. There is also an experimental sign of the topological superconductivity realization in the present structure.

cond-mat.mes-hall↗

arXiv2018

Realization of a double-slit SQUID geometry by Fermi arc surface states in a WTe$_2$ Weyl semimetal

We experimentally study electron transport between two superconducting indium leads, coupled to the WTe$_2$ crystal surface. WTe$_2$ is characterized by presence of Fermi arc surface states, as a predicted type-II Weyl semimetal candidate. We demonstrate Josephson current in unprecedentedly long 5~$μ$m In-WTe$_2$-In junctions, which is confirmed by $I-V$ curves evolution with temperature and magnetic field. The Josephson current is mostly carried by the topological surface states, which we demonstrate in a double-slit SQUID geometry, realized by coupling the opposite WTe$_2$ crystal surfaces.

cond-mat.mes-hall↗

arXiv2017

Proximity-induced superconductivity within the InAs/GaSb edge conducting state

We experimentally investigate Andreev transport through the interface between an indium superconductor and the edge of the InAs/GaSb bilayer. To cover all possible regimes of InAs/GaSb spectrum, we study samples with 10 nm, 12 nm, and 14 nm thick InAs quantum wells. For the trivial case of a direct band insulator in 10~nm samples, differential resistance demonstrates standard Andreev reflection. For InAs/GaSb structures with band inversion (12~nm and 14 nm samples), we observe distinct low-energy structures, which we regard as direct evidence for the proximity-induced superconductivity within the current-carrying edge state. For 14~nm InAs well samples, we additionally observe mesoscopic-like resistance fluctuations, which are subjected to threshold suppression in low magnetic fields.

cond-mat.mes-hall↗

arXiv2017

Conductance oscillations and zero-bias anomaly in a single superconducting junction to a three-dimensional $Bi_2Te_3$ topological insulator

We experimentally investigate Andreev transport through a single junction between an s-wave indium superconductor and a thick film of a three-dimensional $Bi_2Te_3$ topological insulator. We study $Bi_2Te_3$ samples with different bulk and surface characteristics, where the presence of a topological surface state is confirmed by direct ARPES measurements. All the junctions demonstrate Andreev transport within the superconducting gap. For junctions with transparent $In-Bi_2Te_3$ interfaces we find a number of nearly periodic conductance oscillations, which are accompanied by zero-bias conductance anomaly. Both effects disappear above the superconducting transition or for resistive junctions. We propose a consistent interpretation of both effects as originating from proximity-induced superconducting correlations within the $Bi_2Te_3$ topological surface state.

cond-mat.mes-hall↗

arXiv2016

Interlayer current near the edge of an InAs/GaSb double quantum well in proximity with a superconductor

We investigate charge transport through the junction between a niobium superconductor and the edge of a two-dimensional electron-hole bilayer, realized in an InAs/GaSb double quantum well. For the transparent interface with a superconductor, we demonstrate that the junction resistance is determined by the interlayer charge transfer near the interface. From an analysis of experimental $I-V$ curves we conclude that the proximity induced superconductivity efficiently couples electron and hole layers at low currents. The critical current demonstrates periodic dependence on the in-plane magnetic field, while it is monotonous for the field which is normal to the bilayer plane.

cond-mat.mes-hall↗

arXiv2016

Strong coupling between a permalloy ferromagnetic contact and a helical edge channel in a narrow HgTe quantum well

We experimentally investigate spin-polarized electron transport between a permalloy ferromagnet and the edge of a two-dimensional electron system with band inversion, realized in a narrow, 8~nm wide HgTe quantum well. In zero magnetic field, we observe strong asymmetry of the edge potential distribution with respect to the ferromagnetic ground lead. This result indicates, that the helical edge channel, specific for the structures with band inversion even at the conductive bulk, is strongly coupled to the ferromagnetic side contact, possibly due to the effects of proximity magnetization. It allows selective and spin-sensitive contacting of helical edge states.

cond-mat.mes-hall↗

arXiv2016

Specular Andreev reflection at the edge of an InAs/GaSb double quantum well with band inversion

We experimentally investigate transport through the side junction between a niobium superconductor and the mesa edge of a two-dimensional system, realized in an InAs/GaSb double quantum well with band inversion. We demonstrate, that different transport regimes can be achieved by variation of the mesa step. We observe anomalous behavior of Andreev reflection within a finite low-bias interval, which is invariant for both transport regimes. We connect this behavior with the transition from retro- (at low biases) to specular (at high ones) Andreev reflection channels in an InAs/GaSb double quantum well with band inversion.

cond-mat.mes-hall↗