A5080269201- Quantum Information and Cryptography
- Quantum and electron transport phenomena
- Quantum Computing Algorithms and Architecture
- Mechanical and Optical Resonators
- Quantum Mechanics and Applications
- Physics of Superconductivity and Magnetism
- Quantum optics and atomic interactions
- Spectroscopy and Quantum Chemical Studies
- Cold Atom Physics and Bose-Einstein Condensates
- Advanced Thermodynamics and Statistical Mechanics
- Photonic and Optical Devices
- advanced mathematical theories
- Force Microscopy Techniques and Applications
- Advanced MEMS and NEMS Technologies
- Atomic and Subatomic Physics Research
- Quantum, superfluid, helium dynamics
- Surface and Thin Film Phenomena
- Spacecraft and Cryogenic Technologies
- Magnetic Field Sensors Techniques
- Various Chemistry Research Topics
- Quantum chaos and dynamical systems
- Nonlinear Dynamics and Pattern Formation
- Advanced Chemical Physics Studies
- Quantum Electrodynamics and Casimir Effect
- Strong Light-Matter Interactions
IQM (Finland)
2021-2024
Aalto University
2016-2021
University of Oulu
2008-2019
Abstract Coupling electromagnetic waves in a cavity and mechanical vibrations via the radiation pressure of photons is promising platform for investigations quantum–mechanical properties motion. A drawback that effect one photon tends to be tiny, hence pressing challenges substantially increase interaction strength. novel scenario introduce into setup quantum two-level system (qubit), which, besides strengthening coupling, allows rich physics strongly enhanced nonlinearities. Here we present...
We review the physical phenomena that arise when quantum mechanical energy levels are modulated in time. The dynamics resulting from changes transition frequency is a problem studied since early days of mechanics. It has been constant interest both experimentally and theoretically since, with simple two-state model providing an inexhaustible source novel concepts. When system modulated, several can be observed, such as Landau–Zener–Stückelberg–Majorana interference, motional averaging...
Cavity optomechanics is showing promise for studying quantum mechanics in large systems. However, the smallness of radiation-pressure coupling a serious hindrance. Here we show how charge tuning Josephson inductance single-Cooper-pair transistor can be exploited to arrange strong radiation-pressure-type ${g}_{0}$ between mechanical and microwave resonators. In certain limit parameters, such also seen as qubit-mediated two We that this scheme allows reaching extremely high ${g}_{0}$. Contrary...
Tunable coupling of superconducting qubits has been widely studied due to its importance for isolated gate operations in scalable quantum processor architectures. Here, we demonstrate a tunable qubit-qubit coupler based on floating transmon device, which allows us place at least 2 mm apart from each other while maintaining over 50-MHz between the and qubits. In introduced tunable-coupler design, both qubit-coupler couplings are mediated by two waveguides instead relying direct capacitive...
A superconducting qubit was driven in an ultrastrong fashion by oscillatory microwave field, which created coupling via the nonlinear Josephson energy. The observed Stark shifts of ``atomic'' levels are so pronounced that corrections even beyond lowest-order Bloch-Siegert shift needed to properly explain measurements. quasienergies dressed two-level system were probed resonant absorption a cavity, and results agreement with calculation based on Floquet approach.
When the level separation of a qubit is modulated periodically across an avoided crossing, tunneling to excited state—and consequently Landau–Zener–Stückelberg interference—can occur. The types modulation studied so far correspond continuous change separation. Here we study periodic latching modulation, in which switched abruptly between two values and kept constant otherwise. In this case, conventional approach based on asymptotic Landau–Zener formula for transition probabilities not...
Superconducting qubits are one of the most promising candidates to implement quantum computers. The superiority superconducting computers over any classical device in simulating random but well-determined circuits has already been shown two independent experiments and important steps have taken error correction. However, currently wide-spread qubit designs do not yet provide high enough performance enable practical applications or efficient scaling logical owing several following issues:...
We show that the counter-rotating terms of dispersive qubit-cavity Rabi model can produce relatively large and nonmonotonic Bloch-Siegert shifts in cavity frequency as system is driven through a quantum-to-classical transition. Using weak microwave probe tone, we demonstrate experimentally this effect by monitoring resonance coupled to transmon field with varying power. In weakly regime (quantum phase), shift appears small constant shift, while for strong drive (classical phase) it presents...
Abstract We propose an efficient qubit initialization protocol based on a dissipative environment that can be dynamically adjusted. Here, the is coupled to thermal bath through tunable harmonic oscillator. On-demand achieved by sweeping oscillator rapidly into resonance with qubit. This resonant coupling engineered induces fast relaxation ground state of system, and consecutive rapid sweep back off guarantees weak excess dissipation during quantum computations. solve corresponding dynamics...
Superconducting microwave circuits show great potential for practical quantum technological applications such as information processing. However, fast and on-demand initialization of the degrees freedom in these devices remains a challenge. Here, we experimentally implement tunable heat sink that is potentially suitable superconducting qubits. Our device consists two coupled resonators. The first resonator has high quality factor fixed frequency whereas second designed to have low resonance...
We investigate the driven quantum phase transition between oscillating motion and classical nearly free rotations of Josephson pendulum coupled to a harmonic oscillator in presence dissipation. refer this as Josephson-Rabi model. This model describes standard setup circuit electrodynamics, where typically transmon device is embedded superconducting cavity. find that by treating system mechanically occurs at higher drive powers than expected from an all-classical treatment, which consequence...
The present qubit technology, in particular, Josephson qubits, allows an unprecedented control of discrete energy levels. This motivates a new study the old pump-probe problem, where quantum system is driven by strong drive and simultaneously probed weaker one. included Floquet method resulting quasienergy states are then studied with probe. We harmonic has significant longitudinal component relative to static equilibrium state qubit. Both analytical numerical methods used solve problem....
The urgent need for reliable simulation tools to match the extreme accuracy needed control tailored quantum devices highlights importance of understanding open systems and their modeling. To this end, we compare here commonly used Redfield Lindblad master equations against numerically exact results in case one two resonant qubits transversely coupled at a single point Drude-cut ohmic bath. All relevant parameters are varied over broad range, which allows us give detailed predictions about...
We present here our recent results on qubit reset scheme based a quantum-circuit refrigerator (QCR). In particular, we use the photon-assisted quasiparticle tunneling through superconductor--insulator--normal-metal--insulator--superconductor junction to controllably decrease energy relaxation time of during QCR operation. experiment, transmon with dispersive readout. The is capacitively coupled its normal-metal island. employ rapid, square-shaped control voltage pulses durations in range...
This paper presents numerical results on the coupling between qubits and a low-temperature bath. The show that there exist strong gives rise to Lamb shift bath entanglement uncover trade-off speed accuracy. However, this does not pose an issue for execution of quantum gates these can be modeled using standard, weak-coupling approach
The standard weak-coupling approximations associated to open quantum systems have been extensively used in the description of a two-level system, qubit, subjected relatively weak dissipation compared with qubit frequency. However, recent progress experimental implementations controlled increased levels on-demand engineered has motivated precision studies parameter regimes that question validity approximations, especially presence time-dependent drive fields. In this paper, we address by...
Abstract Enhancing the performance of noisy quantum processors requires improving our understanding error mechanisms and ways to overcome them. A judicious selection qubit design parameters plays a pivotal role in processors. In this study, we identify optimal ranges for parameters, grounded comprehensive noise modeling. To end, also analyze effect charge-parity switch caused by quasiparticles on two-qubit gate. Due utilization second excited state transmon, where charge dispersion is...
With advanced fabrication techniques it is possible to make nanoscale electronic structures that have discrete energy levels. Such are called artificial atoms because of analogy with true atoms. Examples such quantum dots in semiconductor heterostructures and Josephson-junction qubits. It also interacting each other. This an molecule the sense states analogous ones a molecule. In this letter we present different type that, addition states, includes analog nuclear vibrations diatomic Some...
We study the novel nonlinear phenomena that emerge in a charge qubit due to interplay between strong microwave flux drive and periodic Josephson potential. first analyse system terms of linear Landau–Zener–Stückelberg model, show its inadequacy with several Landau–Zener crossings within period. Experimentally, we probe quasienergy levels driven an LC cavity, which requires use response theory. also our numerical calculations are good agreement experimental data.
We introduce the diabatic and adiabatic bases of a strongly driven superconducting two-level system. The multiphoton resonance conditions, Rabi couplings, energy levels are calculated in both using rotating wave approximation, results compared with corresponding numerical values. show basis dependence approximate deduce validity regions for bases. demonstrate parameter region where neither is sufficient calculations approximation.
We analyze a superconducting charge qubit that is dispersively coupled to an electric resonator. The system connected transmission line allows reflection measurement. In this paper we derive the equations of motion by using quantum network theory. assume measurement signal so strong resonator behaves classically. time evolution calculated with Bloch equations. have simulated in adiabatic eigenbasis bring out effects changing band curvatures under driving. use circuit theory calculate energy...