arXiv subjects

Byoung-moo Ann

Publications and source records attributed to Byoung-moo Ann.

9 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 $2π\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

All-microwave Lamb shift engineering for a fixed frequency multi-level superconducting qubit

It is known that the electromagnetic vacuum is responsible for the Lamb shift, which is a crucial phenomenon in quantum electrodynamics (QED). In circuit QED, the readout or bus resonators that are dispersively coupled can result in a significant Lamb shift of the qubit. However, previous approaches or proposals for controlling the Lamb shift in circuit QED demand overheads in circuit designs or non-perturbative renormalization of the system's eigenbases, which can impose formidable limitations.In this work, we propose and demonstrate an all-microwave method for controlling the Lamb shift of fixed-frequency transmons. We employ the drive-induced longitudinal coupling between the transmon and resonator. By simply using an off-resonant monochromatic drive near the resonator frequency, we can control the net Lamb shift up to 30 MHz and engineer it to zero with the drive-induced longitudinal coupling without facing the aforementioned challenges. Our work establishes an efficient way of engineering the fundamental effects of the electromagnetic vacuum and provides greater flexibility in non-parametric frequency controls of multilevel systems.

quant-ph↗

arXiv2023

Resolving non-perturbative renormalization of a microwave-dressed weakly anharmonic superconducting qubit

Microwave driving is a ubiquitous technique for superconducting qubits (SCQs), but the dressed states description based on the conventionally used perturbation theory cannot fully capture the dynamics in the strong driving limit. Comprehensive studies beyond these approximations applicable to transmon-based circuit quantum electrodynamics (QED) systems are unfortunately rare as the relevant works have been mainly limited to single-mode or two-state systems. In this work, we investigate a microwave-dressed transmon coupled to a single quantized mode over a wide range of driving parameters. We reveal that the interaction between the transmon and resonator as well as the properties of each mode is significantly renormalized in the strong driving limit. Unlike previous theoretical works, we establish a non-recursive, and non-Floquet theory beyond the perturbative regimes, which excellently quantifies the experiments. This work expands our fundamental understanding of dressed cavity QED-like systems beyond the conventional approximations. Our work will also contribute to fast quantum gate implementation, qubit parameter engineering, and fundamental studies on driven nonlinear systems.

quant-ph↗

arXiv2023

Two-photon sideband transition in a driven quantum Rabi model : Quantitative discussions with derived longitudinal drives and beyond the rotating wave approximation

In this work, we analytically and numerically study the sideband transition dynamics of the driven quantum Rabi model (QRM). We focus in particular on the conditions when the external transverse drive fields induce first-order sideband transitions. Inducing sideband transitions between two different systems is an essential technique for various physical models, including the QRM. However, despite its importance, a precise analytical study has not been reported yet that successfully explains the sideband transition rates in a driven QRM applicable for all system parameter configurations. In our study, we analytically derive the sideband transition rates based on second-order perturbation theory, not relying on the rotating wave approximation (RWA) \cite{RWA}. Our formula are valid for all ranges of drive frequencies and system's parameters. Our analytical derived formula agrees well with the numerical results in a regime of moderate drive amplitudes. Interestingly, we have found a non-trivial longitudinal drive effect derived from the transverse drive Hamiltonian. This accounts for significant corrections to the sideband transition rates that are expected without considering the derived longitudinal effect. Using this approach, one can precisely estimate the sideband transition rates in the QRM not confining themselves within specific parameter regimes. This provides important contributions for understanding experiments described by the driven QRM.

quant-ph↗

arXiv2021

Sideband transitions in a two-mode Josephson circuit driven beyond the rotating wave approximation

Driving quantum systems periodically in time plays an essential role in the coherent control of quantum states. The rotating wave approximation (RWA) is a good approximation technique for weak and nearly-resonance driven fields. However, these experiments sometimes require large detuning and strong driving fields, for which the RWA may not hold. In this work, we experimentally, numerically, and analytically explore strongly driven two-mode Josephson circuits in the regime of strong driving and large detuning. Specifically, we investigate beam-splitter and two-mode squeezing interaction between the two modes induced by driving a two-photon sideband transition. Using numerical simulations, we observe that the RWA is unable to correctly capture the amplitude of the sideband transition rates. We verify this finding using an analytical model that is based on perturbative corrections. We find that the breakdown of the RWA in the regime studied does not lead to qualitatively different dynamics, but gives the same results as the RWA theory at higher drive strengths, enhancing the coupling rates compared to what one would predict. This is an interesting consequence compared to the carrier transition case, where the breakdown of the RWA results in qualitatively different time evolution of the quantum state. Our work provides an insight into the behavior of time-periodically driven systems beyond the RWA. We also provide a robust theoretical framework for including these findings in the calculation and calibration of quantum protocols in circuit quantum electrodynamics.

quant-ph↗

arXiv2021

Motional resonances of three-dimensional dual-species Coulomb crystals

We investigate the motional resonances of dual-species Coulomb crystals comprised of $^9$Be$^+$ and $^{24}$Mg$^+$ ions held in a 4-rod linear Paul trap. Our experimental data and simulations show that the secular motion of such mixed crystals has rich dynamics. Their secular spectra can differ significantly from those of pure ion crystals. We propose a simple model based on mechanical coupling with Coulomb interactions between the two different ion species that explains many features of the secular spectrum. Our findings contribute to a more reliable identification of the ion species in mixed crystals.

physics.atom-ph↗

arXiv2020

Tuneable and weakly-invasive probing of a superconducting resonator based onelectromagnetically induced transparency

Superconducting cavities with high quality factors play an essential role in circuit quantum electrodynamics and quantum computing. In measurements of the the intrinsic loss rates of high frequency modes, it can be challenging to design an appropriate coupling to the measurement circuit in such a way that the resulting signal is sufficiently strong but also that this coupling does not lead to unwanted loading circuit, obscuring the intrinsic internal loss rates. Here, we propose and demonstrate a spectroscopic probe of high-Q resonators based on the phenomena of electromagnetically-induced transparency (EIT) between the resonator and qubit in the weak dispersive coupling regime. Applying a sideband drive signal to the qubit, we observe an interference dip originated from EIT in the qubit spectroscopy, originating from the quantum interference between the qubit probe signal and sideband transition. From the width and the depth of the dip, we are able to extract the single-photon linewidth of the resonator from an analytical model. Working in a previously unexplored regime in which the qubit has a larger linewidth than the resonator reduces the technical challenge of making a high-coherence qubit and is advantageous for remaining in the weakly-invasive limit of coupling to the resonator. Furthermore, the sideband and the dispersive coupling between the resonator and the qubit can be tuned $in~situ$ controlling the strength of the sideband drive power. This $in-situ$ tuneability allows the technique to be applied for efficient measurement of the resonator loss rate for any quality factor below a fixed upper bound, on the order of $10^8$ for our device, allowing a wide range of quality factors to probed using a single design.

quant-ph↗

arXiv2019

Observation of scalable sub-Poissonian-field lasing in a microlaser

Sub-Poisson field with much reduced fluctuations in a cavity can boost quantum precision measurements via cavity-enhanced light-matter interactions. Strong coupling between an atom and a cavity mode has been utilized to generate highly sub-Poisson fields. However, a macroscopic number of optical intracavity photons with more than 3dB variance reduction in a setting of laser has not been possible. Here, we report sub-Poisson field lasing in a microlaser operating with hundreds of atoms with well-regulated atom-cavity coupling and interaction time. Its photon-number variance was 4dB below the standard quantum limit while the intracavity mean photon number scalable up to 600. The highly sub-Poisson photon statistics were not deteriorated by simultaneous interaction of a large number of atoms. Our finding suggests an effective pathway to widely scalable quasi-Fock-state lasing at the macroscopic scale.

quant-ph↗

arXiv2015

Correction to the detector-dead-time effect on the second-order correlation of stationary sub-Poissonian light in a two-detector configuration

Exact measurement of the second-order correlation function $g^{(2)}(t)$ of a light source is essential when investigating the photon statistics and the light generation process of the source. For a stationary single-mode light source, Mandel Q factor is directly related to $g^{(2)}(t)$. For a large mean photon number in the mode, the deviation of $g^{(2)}(t)$ from unity is so small that even a tiny error in measuring $g^{(2)}(t)$ would result in an inaccurate Mandel Q. In this work, we have found that detector dead time can induce a serious error in $g^{(2)}(t)$ and thus in Mandel Q in those cases even in a two-detector configuration. Our finding contradicts the conventional understanding that detector dead time would not affect $g^{(2)}(t)$ in two-detector configurations. Utilizing the cavity-QED microlaser, a well-established sub-Poissonian light source, we measured $g^{(2)}(t)$ with two different types of photodetectors with different dead time. We also introduced prolonged dead time by intentionally deleting the photodetection events following a preceding one within a specified time interval. We found that the observed Q of the cavity-QED microlaser was underestimated by 19% with respect to the dead-time-free Q when its mean photon number was about 600. We derived an analytic formula which well explains the behavior of the $g^{(2)}(t)$ as a function of the dead time.

physics.optics↗