arXiv subjects

F. Balestro

Publications and source records attributed to F. Balestro.

12 recordsLinked to original sources

arXiv2026

A material-agnostic platform to probe spin-phonon interactions using high-overtone bulk acoustic wave resonators

Spin-phonon interactions have a dual role in emerging spin-based quantum technologies. While they can be a limitation to device performance through decoherence, they also serve as a critical resource for coherent spin control, detection, and the realization of spin-based quantum networks. However, their direct characterization remains a challenge and is usually material-dependent. Here, we introduce a technique to probe spin-phonon coupling at millikelvin temperatures and gigahertz frequencies, using high-overtone bulk acoustic wave resonators (HBARs) integrated with arbitrary crystals via visco-elastic transfer of thin-film lithium niobate transducers. By tuning the Larmor frequency of dilute spin ensembles into resonance with HBAR modes, we extract the anisotropy and strength of spin-phonon interactions from acoustic dispersion and dissipation measurements. We demonstrate this approach in calcium tungstate (CaWO4) and yttrium orthosilicate (Y2SiO5), achieving cooperativities up to 0.5 for erbium dopant ensembles. Our method enables the study of spin-phonon interactions in complex crystalline materials, with minimal fabrication constraints. These results will facilitate the design of hybrid quantum systems and the quest for ion-matrix combination with enhanced spin-phonon coupling.

cond-mat.mes-hall↗

arXiv2025

Approaching optimal microwave-acoustic transduction on lithium niobate using SQUID arrays

Electronic devices exploiting acoustic vibrations are ubiquitous in classical and quantum technologies. Central to these devices is the transducer, which enables the exchange of signals between electrical and acoustic networks. Among the various transduction mechanisms, piezoelectricity remains the most widely used. However, conventional piezoelectric transducers are limited to either small efficiencies or narrow bandwidths and they typically operate at fixed frequency. These limitations restrict their utility in many applications. Here we propose and demonstrate a robust strategy to realize piezoelectric microwave-acoustic transduction close to the maximal efficiency-bandwidth product of lithium niobate. We use SQUID arrays to transform the large complex impedance of wide-band interdigital transducers into 50 $\Omega$ and demonstrate unprecedented efficiency$\times$bandwidth $\approx$ 440 MHz, with a maximum efficiency of 62% at 5.7 GHz. Moreover, leveraging the flux dependence of SQUIDs, we realize transducers with in-situ tunability across nearly an octave around 5.5 GHz. Our transducer can be readily connected to other superconducting quantum devices, with applications in microwave-to-optics conversion schemes, quantum-limited phonon detection, or acoustic spectroscopy in the 4-8 GHz band.

cond-mat.mes-hall↗

arXiv2017

Landau-Zener transition in a continuously measured single-molecule spin transistor

We monitor the Landau-Zener dynamics of a single-ion magnet in a spin-transistor geometry. For increasing field-sweep rates, the spin reversal probability shows increasing deviations from that of a closed system. In the low-conductance limit, such deviations are shown to result from a dephasing process. In particular, the observed behaviors are succesfully simulated by means of an adiabatic master equation, with time averaged dephasing (Lindblad) operators. The time average is tentatively interpeted in terms of the finite time resolution of the continuous measurement.

cond-mat.mes-hall↗

arXiv2009

Superconductivity in a single C60 transistor

Single molecule transistors (SMTs) are currently attracting enormous attention as possible quantum information processing devices. An intrinsic limitation to the prospects of these however is associated to the presence of a small number of quantized conductance channels, each channel having a high access resistance of at best $R_{K}/2=h/2e^{2}$=12.9 k$\Omega$. When the contacting leads become superconducting, these correlations can extend throughout the whole system by the proximity effect. This not only lifts the resistive limitation of normal state contacts, but further paves a new way to probe electron transport through a single molecule. In this work, we demonstrate the realization of superconducting SMTs involving a single C60 fullerene molecule. The last few years have seen gate-controlled Josephson supercurrents induced in the family of low dimensional carbon structures such as flakes of two-dimensional graphene and portions of one-dimensional carbon nanotubes. The present study involving a full zero-dimensionnal fullerene completes the picture.

cond-mat.mes-hall↗

arXiv2008

Kondo effects in a C_60 single-molecule transistor

We have used the electromigration technique to fabricate a $\rm{C_{60}}$ single-molecule transistor (SMT). We present a full experimental study as a function of temperature, down to 35 mK, and as a function of magnetic field up to 8 T in a SMT with odd number of electrons, where the usual spin-1/2 Kondo effect occurs, with good agreement with theory. In the case of even number of electrons, a low temperature magneto-transport study is provided, which demonstrates a Zeeman splitting of the zero-bias anomaly at energies well below the Kondo scale.

cond-mat.mes-hall↗

arXiv2006

Using a quantum dot as a high-frequency shot noise detector

We present the experimental realization of a Quantum Dot (QD) operating as a high-frequency noise detector. Current fluctuations produced in a nearby Quantum Point Contact (QPC) ionize the QD and induce transport through excited states. The resulting transient current through the QD represents our detector signal. We investigate its dependence on the QPC transmission and voltage bias. We observe and explain a quantum threshold feature and a saturation in the detector signal. This experimental and theoretical study is relevant in understanding the backaction of a QPC used as a charge detector.

cond-mat.mes-hall↗

arXiv2005

Shot Noise Detection on a Carbon Nanotube Quantum Dot

An on-chip detection scheme for high frequency signals is used to detect noise generated by a quantum dot formed in a single wall carbon nanotube. The noise detection is based on photon assisted tunneling in a superconductor-insulator-superconductor junction. Measurements of shot noise over a full Coulomb diamond are reported with excited states and inelastic cotunneling clearly resolved. Super-Poissonian noise is detected in the case of inelastic cotunneling.

cond-mat.mes-hall↗

arXiv2004

Coherent oscillations in a superconducting multi-level quantum system

We have observed coherent time evolution of states in a multi-level quantum system, formed by a current-biased dc SQUID. The manipulation of the quantum states is achieved by resonant microwave pulses of flux. The number of quantum states participating in the coherent oscillations increases with increasing microwave power. Quantum measurement is performed by a nanosecond flux pulse which projects the final state onto one of two different voltage states of the dc SQUID, which can be read out.

cond-mat.supr-con↗

arXiv2003

One-shot quantum measurement using a hysteretic DC-SQUID

We propose a single shot quantum measurement to determine the state of a Josephson charge quantum bit (qubit). The qubit is a Cooper pair box (CPB) and the measuring device is a two junction superconducting quantum interference device (dc-SQUID). This coupled system exhibits a close analogy with a Rydberg atom in a high Q cavity, except that in the present device we benefit from the additional feature of escape from the supercurrent state by macroscopic quantum tunneling, which provides the final read-out. We test the feasibility of our idea against realistic experimental circuit parameters and by analyzing the phase fluctuations of the qubit.

cond-mat.supr-con↗

arXiv2003

Evidence of two-dimensional macroscopic quantum tunneling of a current-biased DC-SQUID

The escape probability out of the superconducting state of a hysteretic DC-SQUID has been measured at different values of the applied magnetic flux. At low temperature, the escape current and the width of the probability distribution are temperature independent but they depend on flux. Experimental results do not fit the usual one-dimensional (1D) Macroscopic Quantum Tunneling (MQT) law but are perfectly accounted for by the two-dimensional (2D) MQT behaviour as we propose here. Near zero flux, our data confirms the recent MQT observation in a DC-SQUID \cite{Li02}.

cond-mat.supr-con↗

arXiv2002

Cooper Pair Box Coupled to a Current-Biased Josephson Junction

We study the dynamics of a quantum superconducting circuit which consists of a Josephson charge qubit, coupled capacitively to a current biased Josephson junction. Under certain conditions, the eigenstates of the qubit and the junction become entangled. We obtain the time evolution of these states in the limit of weak coupling. Rabi oscillations occur, as a result of the spontaneous emission and re-absorption of a single oscillation quantum in the junction. We discuss a possible way to experimentally determine the quantum state of the junction and hence observe the Rabi oscillations.

cond-mat.supr-con↗

arXiv2000

First experimental evidence of one-dimensional plasma modes in superconducting thin wires

We have studied niobium superconducting thin wires deposited onto a SrTiO$_{3}$ substrate. By measuring the reflection coefficient of the wires, resonances are observed in the superconducting state in the 130 MHz to 4 GHz range. They are interpreted as standing wave resonances of one-dimensional plasma modes propagating along the superconducting wire. The experimental dispersion law, $ω$ versus $q$, presents a linear dependence over the entire wave vector range. The modes are softened as the temperature increases close the superconducting transition temperature. Very good agreement are observed between our data and the dispersion relation predicted by Kulik and Mooij and Schön.

cond-mat.mes-hall↗