A5111760858- Quantum Information and Cryptography
- Quantum and electron transport phenomena
- Quantum Computing Algorithms and Architecture
- Quantum optics and atomic interactions
- Physics of Superconductivity and Magnetism
- Quantum Mechanics and Applications
- Topological Materials and Phenomena
- Quantum many-body systems
- Cold Atom Physics and Bose-Einstein Condensates
- Mechanical and Optical Resonators
- Spectroscopy and Quantum Chemical Studies
- Atomic and Subatomic Physics Research
- Quantum, superfluid, helium dynamics
- Advanced Condensed Matter Physics
- Advanced NMR Techniques and Applications
- Rare-earth and actinide compounds
- Laser-Matter Interactions and Applications
- Quantum chaos and dynamical systems
- Quantum-Dot Cellular Automata
- Advanced Thermodynamics and Statistical Mechanics
- Amyloidosis: Diagnosis, Treatment, Outcomes
- Neutrino Physics Research
- Mathematical Analysis and Transform Methods
- Complex Systems and Time Series Analysis
- Quantum Electrodynamics and Casimir Effect
Landau Institute for Theoretical Physics
2008-2025
National Research University Higher School of Economics
2017-2025
Moscow Institute of Physics and Technology
2010-2016
Aalto University
2010-2014
Physikalisch-Technische Bundesanstalt
2011
Lomonosov Moscow State University
2011
Karlsruhe Institute of Technology
1999-2007
Karlsruhe University of Education
2000-2006
Laboratoire de Physique de l'ENS de Lyon
2004
École Normale Supérieure de Lyon
2004
We review recent theoretical and experimental progress in quantum state engineering with Josephson junction devices. The concepts of computing have stimulated an increased activity the field. Either charges or phases (fluxes) systems can be used as degrees freedom, their manipulated coherently by voltage current pulses. They thus serve qubits, logic gates performed. Their phase coherence time, which is limited, e.g., electromagnetic fluctuations control circuit, long enough to allow a series...
Decoherence in quantum bit circuits is presently a major limitation to their use for computing purposes. We present experiments, inspired from NMR, that characterise decoherence particular superconducting circuit, the quantronium. introduce general framework analysis of decoherence, based on spectral densities noise sources coupled qubit. Analysis our measurements within this indicates simple model acting discuss various methods fight decoherence.
Landau-Zener (LZ) tunneling can occur with a certain probability when crossing energy levels of quantum two-level system are swept across the minimum separation. Here we present experimental evidence interference effects in solid-state LZ tunneling. We used Cooper-pair box qubit where occurs at charge degeneracy. By employing weak nondemolition monitoring, observe between consecutive LZ-tunneling events; find that average level occupancies depend on dynamical phase. The system's unusually...
1/f noise, the major source of dephasing in Josephson qubits, may be produced by an ensemble two-level systems. Depending on statistical properties their distribution, noise distribution can Gaussian or non-Gaussian. The latter situation is realized, for instance, when coupling strengths has a slowly decaying power-law tail. In this regime, questions self-averaging and sample-to-sample fluctuations become crucial. We study process class functions analyse results.
Motivated by recent experiments with Josephson-junction circuits, we analyze the influence of various noise sources on dynamics two-level systems at optimal operation points where linear coupling to low-frequency fluctuations is suppressed. We study decoherence due nonlinear (quadratic) coupling, focusing experimentally relevant $1/f$ and Ohmic power spectra. For strong higher-order effects evolution.
Recent experiments indicate a connection between the low- and high-frequency noise affecting superconducting quantum systems. We explore possibilities that both noises can be produced by one ensemble of microscopic modes, made up, e.g., sufficiently coherent two-level systems (TLS). This implies relation power in different frequency domains, which depends on distribution parameters TLSs. show distribution, natural for tunneling TLSs, with log-uniform tunnel splitting linear bias, accounts...
Motivated by recent experiments with Josephson-junction circuits we reconsider decoherence effects in quantum two-level systems (TLS). On one hand, the demonstrate importance of 1/f noise, on other operating at symmetry points can suppress noise linear order. We, therefore, analyze sources a variety power spectra, or quadratic coupling, which are longitudinal transverse relative to eigenbasis unperturbed Hamiltonian. To evaluate dephasing time for second-order contributions have be taken...
We study noise-related properties of current in adiabatic pumps. A symmetry the problem allows us to relate statistics charge transport case one-channel leads geometry loops on a sphere (for many channels higher-dimensional manifold). This provides unifying framework, which simplifies analysis various realizations For each pumping cycle, average and its minimal variance are given by areas enclosed corresponding loop surface (soap film) spanned this loop. formulate conditions for quantization...
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.
We investigate the geometric phase or Berry acquired by a spin half which is both subject to slowly varying magnetic field and weakly coupled dissipative environment (either quantum classical). study how this modified find that modification of nature. While original (for an isolated system) flux monopole through loop traversed field, environment-induced quadrupolelike field. complex, its imaginary part contribution dephasing. Its sign depends on direction loop. Unlike phase, dephasing gauge...
The quantum measurement process by a single-electron transistor or point contact coupled to bit is studied. We find unified description of the statistics monitored quantity, current, in regime strong and expect this apply for wide class measurements. derive probability distributions current charge different stages process. In parameter develops telegraph-noise behavior which can be detected noise spectrum.
In the Majorana representation of a spin 1/2 we find an identity which relates spin-spin correlators to one-particle fermionic correlators. This should be contrasted with straightforward approach in two-particle (four-fermion) need calculated. We discuss applications analysis dynamics coupled dissipative environment and quantum detector performing continuous measurement qubit's state.
Recent experiments on planar superconductor-topological insulator-superconductor (S-TI-S) junctions, e.g., in the Corbino geometry, have reported low-temperature nonzero Josephson currents states with integer fluxoid (flux) induced junction by a perpendicular magnetic field. This effect was discussed connection Majorana zero modes localized vortices of such junctions. Here, we provide an explanation for this phenomenon, attributing it to imperfections. We focus “atomic” limit which...
We investigate the energy relaxation $({T}_{1})$ process of a qubit coupled to bath dissipative two-level fluctuators (TLFs). consider strongly both in limit spectrally sparse single TLFs as well dense TLFs. conclude that avoided level crossings, usually attributed very TLFs, could also be caused by many weakly fluctuators.
We analyze the control of Majorana zero-energy states by mapping fermionic system onto a chain Ising spins. Although topological protection is lost for system, provides additional insight into nature quantum states. By controlling local magnetic field, one can separate ferromagnetic and paramagnetic phases, corresponding to nontopological sections system. In this paper we propose (topologically nonprotected) protocols performing braiding operation, in fact also more general rotations. first...
We provide topological classification of possible phases with the symmetry planar phase superfluid $^{3}\mathrm{He}$. Compared to B [class DIII in A. Altland and M. R. Zirnbauer, Phys. Rev. 55, 1142 (1997)], it has an additional symmetry, which modifies topology. analyze topology terms explicit mappings from momentum space also discuss explicitly invariants for phase. further show how bulk-boundary correspondence three-dimensional (3D) can be inferred that 2D A general condition is derived...
We analyze the coupling of qubits mediated by a tunable and fast element beyond adiabatic approximation. The nonadiabatic corrections are important even dominant in parts relevant parameter range. As an example, we consider capacitive between two charge gated Josephson junction, as suggested Averin Bruder. nonadiabatic, inductive contribution persists when is tuned to zero. On other hand, total can be turned off (in rotating wave approximation) if operated at symmetry points.
The celebrated Jordan-Wigner transformation provides an efficient mapping between spin chains and fermionic systems in one dimension. Here we extend this spin-fermion to arbitrary tree structures, which enables with nearest-neighbor coupling. is achieved the help of additional spins at junctions one-dimensional chains. This property allows for straightforward simulation Majorana braiding or qubit systems.
The INSQUID (INductive Superconducting QUantum Interference Device) can measure the flux state of a superconducting qubit rapidly, while allowing quantum to evolve with low levels back action. consists dc SQUID unshunted junctions connected in parallel inductor; is placed inside loop. inductor coupled readout resistively-shunted junctions. By applying appropriate fluxes input and inductor, be turned "off", so that virtually no noise from qubit. Different biases turn "on", enabling also used...
We propose a threshold detector with an operating principle based on parametric period-doubling bifurcation in externally pumped nonlinear resonance circuit. The ac-driven circuit includes dc-current--biased Josephson junction ensuring frequency conversion (period-doubling bifurcation) due to its quadratic nonlinearity. A sharp onset of oscillations at the half-frequency drive allows for detection small variations effective inductance and, therefore, readout quantum state coupled qubit....
In this paper we resolve a contradiction between the fact that method based on Majorana representation of spin-$\frac{1}{2}$ is exact and its failure to reproduce perturbative Bloch-Redfield relaxation rates. Namely, for spin-boson model, direct application in leading order allows straightforward computation transverse spin correlations; however, longitudinal correlations it apparently fails long-time limit. Here indicate reason failure. Moreover, suggest how apply allow, nevertheless,...