arXiv subjects

Junho Suh

Publications and source records attributed to Junho Suh.

11 recordsLinked to original sources

arXiv2025

Evidence for unexpectedly low quasiparticle generation rates across Josephson junctions of driven superconducting qubits

Recent studies find that even drives far below the superconducting gap frequency may cause drive-induced quasiparticle generation (QPG) across Josephson junctions (JJs) of superconducting qubits (SCQs), posing a serious concern for fault-tolerant superconducting quantum computing (FTSQC). Nonetheless, quantitative experimental estimation on QPG rates has remained vague. Here, we investigate QPG using strongly driven SCQs, reaching qubit drive amplitudes up to $2\pi\times$300 GHz by applying intense drive fields through the readout resonators. The resonator nonlinear responses enable quantification of the energy loss at SCQs, including the contribution from QPG. Surprisingly, the estimated total energy loss rates are far lower than those expected by the Floquet-Markov formalism with QPG as the sole loss mechanism. Meanwhile, calculations that incorporate high-frequency cutoffs (HFCs) in the QPG conductance at approximately 17-20 GHz effectively explain the experimental observations. These results suggest limitations in either the QPG conductance model or the Markovian treatment of the QPG processes. Both possibilities possess crucial implications for handling QPG problems toward FTSQC and for a more deeper understanding of Josephson junctions.

quant-ph↗

arXiv2025

Simultaneous generation and transfer of mechanical noise squeezing

Optomechanical interactions between mechanical oscillators and an electromagnetic field induce controllable modifications in mechanical fluctuation. When multiple mechanical oscillators are coupled to a single electromagnetic mode, these interactions can be extended to utilize the electromagnetic mode as a mediator for distributing noise squeezing among different mechanical oscillators. We investigate the transfer of mechanical noise squeezing between two mechanical modes, enabled by a single microwave cavity mode which is strongly coupled to both mechanical modes. Noise squeezing in one mechanical mode (control) is achieved through parametric modulation of its resonance frequency via the optical spring effect. Simultaneously, optomechanical beam-splitter interaction is applied between the mechanical modes to transfer noise squeezing from the control mode to the other mode (target). Strong correlations between the quadratures of the two mechanical modes confirm that the observed squeezing in the target mode originates from the squeezing in the control mode. Remarkably, the observed squeezing transfer manifests noise characteristics of both single-mode and two-mode squeezing. This unique feature suggests that the squeezing transfer holds significant potential for enhancing precision measurements.

quant-ph↗

arXiv2025

Effect of Magnetic Anisotropy on Magnetoelastic Waves in Ni/LiNbO3 Hybrid Device

We study the effects of magnetic anisotropy and crystalline axes in surface acoustic waves (SAWs) driven magnetic resonances of Ni/LiNbO3 hybrid devices. SAW absorption from the interaction with magnons in Ni displays a strong anisotropic dependence on the direction of the applied in-plane magnetic field. Magnetic anisotropy is further investigated by magneto-optical Kerr effect measurements to show both uniaxial and biaxial anisotropy components in Ni films on LiNbO3. By introducing a dipolar interaction term in addition to the anisotropies, we successfully explain the anisotropic SAW absorption in our devices. These findings show the importance of substrate-induced anisotropy and long-range dipolar effects in SAW-magnons hybrid devices and indicate future directions for optimizing these spin-acoustic devices through comprehensive anisotropy engineering.

cond-mat.mes-hall↗

arXiv2025

Non-Exponential Relaxation in the Rotating Frame of a Driven Nanomechanical Mode

We present direct observation of the ring-down dynamics in the rotating frame of a resonantly driven single-mode nonlinear nanomechanical resonator. An additional close to resonance harmonic force excites nonlinear oscillations about the fixed point in the rotating frame. When the secondary drive is removed, we measure decay of the in-phase and quadrature components toward this fixed point. We show that the decay of the in-phase signal is non-exponential, even though the vibration amplitude decays exponentially if both forces are switched off. A minimalistic model captures these dynamics as well as the spectrum of the vibrations excited by the additional force, relating them to the dissipation-induced symmetry breaking of the dynamics in the rotating frame.

cond-mat.mes-hall↗

arXiv2024

Electric Control of Polarity in Spin-Orbit Josephson Diode

The effect of spin-orbit coupling in a Josephson diode has not been elucidated due to its interplay with the complexity of Josephson devices. Here, we systematically control local electric fields in epitaxial Al-InAs Josephson junctions under in-plane magnetic fields and observe a polarity reversal of the Josephson diode. We interpret this polarity reversal as an effect of field-tunable spin-orbit coupling on nonreciprocal Josephson currents. A theoretical model, accounting for Rashba and Dresselhaus spin-orbit couplings in a planar Josephson junction containing many transverse subbands, aligns with the observed polarity reversal and its dependence on magnetic field. Our finding addresses spin-orbit control in a Josephson diode, enabling manipulation of Josephson harmonics.

cond-mat.supr-con↗

arXiv2024

Diamond molecular balance: Revolutionizing high-resolution mass spectrometry from MDa to TDa at room temperature

The significance of mass spectrometry lies in its unparalleled ability to accurately identify and quantify molecules in complex samples, providing invaluable insights into molecular structures and interactions. Here, we leverage diamond nanostructures as highly sensitive mass sensors by utilizing a self-excitation mechanism under an electron beam in a conventional scanning electron microscope (SEM). The diamond molecular balance (DMB) exhibits an exceptional mass resolution of 0.36 MDa, based on its outstanding mechanical quality factor and frequency stability, along with an extensive dynamic range from MDa to TDa. This positions the DMB at the forefront of molecular balances operating at room temperature. Notably, the DMB demonstrates its ability to measure the mass of a single bacteriophage T4 by precisely locating the analyte on the device. These findings highlight the groundbreaking potential of the DMB as a revolutionary tool for mass spectrometry at room temperature.

cond-mat.mes-hall↗

arXiv2020

Superconducting Nanoelectromechanical Transducer Resilient to Magnetic Fields

Nanoscale electromechanical coupling provides a unique route towards control of mechanical motions and microwave fields in superconducting cavity electromechanical devices. Though their successes in utilizing the optomechanical or electromechanical back-action effects for various purposes, aluminum imposes severe constraints on their operating conditions with its low superconducting critical temperature (1.2 K) and magnetic field (0.01 T). To extend the potential of the devices, here we fabricate a superconducting electromechanical device employing niobium and demonstrate a set of cavity electromechanical dynamics including back-action cooling and amplification, and electromechanically induced reflection at 4.2 K and in strong magnetic fields up to 0.8 T. This device could be used to realize electromechanical microwave components for quantum technologies by integrating amplifiers, converters, and circulators on a single chip that can be installed at the 4K stage of dilution refrigerators. Moreover, with its ability to control and readout nanomechanical motions simultaneously, this niobium electromechanical transducer could provide powerful nanomechanical sensing platforms.

physics.app-ph↗

arXiv2019

Nanomechanical characterization of quantum interference in a topological insulator nanowire

The discovery of two-dimensional gapless Dirac fermions in graphene and topological insulators (TI) has sparked extensive ongoing research toward applications of their unique electronic properties. The gapless surface states in three-dimensional insulators indicate a distinct topological phase of matter with a non-trivial Z2 invariant that can be verified by angle-resolved photoemission spectroscopy or magnetoresistance quantum oscillation. In TI nanowires, the gapless surface states exhibit Aharonov-Bohm (AB) oscillations in conductance, with this quantum interference effect accompanying a change in the number of transverse one-dimensional modes in transport. Thus, while the density of states (DOS) of such nanowires is expected to show such AB oscillation, this effect has yet to be observed. Here, we adopt nanomechanical measurements that reveal AB oscillations in the DOS of a topological insulator. The TI nanowire under study is an electromechanical resonator embedded in an electrical circuit, and quantum capacitance effects from DOS oscillation modulate the circuit capacitance thereby altering the spring constant to generate mechanical resonant frequency shifts. Detection of the quantum capacitance effects from surface-state DOS is facilitated by the small effective capacitances and high quality factors of nanomechanical resonators, and as such the present technique could be extended to study diverse quantum materials at nanoscale.

cond-mat.mes-hall↗

arXiv2018

Dissipation-driven nonclassical state generation in optomechanics with squeezed light

We study an optomechanical system for the purpose of generating a nonclassical mechanical state when a mechanical oscillator is quadratically coupled to a single-mode cavity field driven by a squeezed optical field. The system corresponds to a regime where the optical dissipation dominates both the mechanical damping and the optomechanical coupling. We identify that multi-phonon processes emerge in the optomechanical system and show that a mechanical oscillator prepared in the ground state will evolve into an amplitude-squared squeezed vacuum state. The Wigner distribution of the steady state of the mechanical oscillator is non-Gaussian exhibiting quantum interference and four-fold symmetry. This nonclassical mechanical state, generated via reservoir engineering, can be used for quantum correlation measurements of the position and momentum of the mechanics below the standard quantum limit.

quant-ph↗

arXiv2018

Interplay between superconductivity and magnetism in one-unit-cell LaAlO3 capped with SrTiO3

To form a conducting layer at the interface between the oxide insulators LaAlO3 and SrTiO3, the LaAlO3 layer on the SrTiO3 substrate must be at least four unit-cells-thick. The LaAlO3 SrTiO3 heterointerface thus formed exhibits various intriguing phenomena such as ferromagnetism and superconductivity. It has been widely studied for being a low-dimensional ferromagnetic oxide superconducting system with a strong gate-tunable spin-orbit interaction. However, its lack of stability and environmental susceptiveness have been an obstacle to its further experimental investigations and applications. Here, we demonstrate that capping the bilayer with SrTiO3 relieves this thickness limit, while enhancing the stability and controllability of the interface. In addition, the SrTiO3-capped LaAlO3 exhibits unconventional superconductivity; the critical current dramatically increases under a parallel magnetic field, and shows a reversed hysteresis contrary to the conventional hysteresis of magnetoresistance. Its superconducting energy gap of $Δ\sim 1.31k_BT_c$ also deviates from conventional BCS-type superconductivity. The oxide trilayer could be a robust platform for studying the extraordinary interplay of superconductivity and ferromagnetism at the interface electron system between LaAlO3 and SrTiO3.

cond-mat.mes-hall↗

arXiv2016

Directly Detecting the Edge Current in a $p_x + ip_y$ Topological Superfluid

Topological superconductors are one of the most actively studied materials these days. They are a promising candidate for hosting Majorana fermions either on their boundaries or in vortex cores. Detecting 1D edge current around the periphery of a 2D $p_x + ip_y$ superconductor would be a hallmark signature of topological superconductivity, but Majorana fermions are not amenable to electronic current measurements due to their charge neutral nature. Thermal conductivity measurements, such as thermal Hall effect, are alternatively proposed, but material synthesis must come first. Superfluid $^3$He-$A$, on the other hand, is a known $p_x + ip_y$ superfluid whose edge current can be measured with a gyroscopic technique. Here, we propose a microelectromechanical system based gyroscope that will not only have enough signal sensitivity to measure the edge current but also be used to observe dimensionality induced phase transitions between different topological superfluids.

cond-mat.supr-con↗