arXiv subjects

M. I. Dykman

Publications and source records attributed to M. I. Dykman.

At least 109 records · Page 6Linked to original sources

arXiv2003

Low-frequency conductivity of a non-degenerate 2D electron liquid in strong magnetic fields

We study the conductivity of a nondegenerate 2D electron liquid in a quantizing magnetic field for frequencies well below the cyclotron frequency. The conductivity is formed by electron transitions in which the energy of a photon goes to the interaction energy of the many-electron system, whereas the involved momentum is transferred to quenched disorder. The conductivity peak is non-Lorentzian. Its shape depends on the relation between the correlation length r_c of the disorder potential and the typical amplitude delta_f of vibrations of the electrons about their quasi-equilibrium positions in the liquid. The width of the peak is determined by the reciprocal time it takes an electron to move over r_c (or the magnetic length l, for r_c< l). In turn, this time is determined by vibrational or diffusive motion, depending on the ratio r_c/delta_f. We analyze the tail of the conductivity peak for short-range disorder. It is formed by multiple collisions with the disorder potential. We also analyze scattering by rare negatively charged traps and show that the conductivity spectrum in this case depends on both short- and long-time electron dynamics.

cond-mat.mes-hall↗

arXiv2002

Qubits with electrons on liquid helium

We study dissipation effects for electrons on the surface of liquid helium, which may serve as qubits of a quantum computer. Each electron is localized in a 3D potential well formed by the image potential in helium and the potential from a submicron electrode submerged into helium. We estimate parameters of the confining potential and characterize the electron energy spectrum. Decay of the excited electron state is due to two-ripplon scattering and to scattering by phonons in helium. We identify mechanisms of coupling to phonons and estimate contributions from different scattering mechanisms. Even in the absence of a magnetic field we expect the decay rate to be $\alt 10^4$ s$^{-1}$. We also calculate the dephasing rate, which is due primarily to ripplon scattering off an electron. This rate is $\alt 10^2$ s$^{-1}$ for typical operation temperatures.

cond-mat.mes-hall↗

arXiv2002

Universality in escape from a modulated potential well

We show that the rate of activated escape $W$ from a periodically modulated potential displays scaling behavior versus modulation amplitude $A$. For adiabatic modulation of an optically trapped Brownian particle, measurements yield $\ln W\propto (A_{\rm c} - A)^μ$ with $μ= 1.5$. The theory gives $μ=3/2$ in the adiabatic limit and predicts a crossover to $μ=2$ scaling as $A$ approaches the bifurcation point where the metastable state disappears.

cond-mat.mes-hall↗

arXiv2001

Activated escape of periodically driven systems

We discuss activated escape from a metastable state of a system driven by a time-periodic force. We show that the escape probabilities can be changed very strongly even by a comparatively weak force. In a broad parameter range, the activation energy of escape depends linearly on the force amplitude. This dependence is described by the logarithmic susceptibility, which is analyzed theoretically and through analog and digital simulations. A closed-form explicit expression for the escape rate of an overdamped Brownian particle is presented and shown to be in quantitative agreement with the simulations. We also describe experiments on a Brownian particle optically trapped in a double-well potential. A suitable periodic modulation of the optical intensity breaks the spatio-temporal symmetry of an otherwise spatially symmetric system. This has allowed us to localize a particle in one of the symmetric wells.

cond-mat.stat-mech↗

arXiv2001

A quantum computer based on electrons floating on liquid helium

Electrons on a helium surface form a quasi two-dimensional system which displays the highest mobility reached in condensed matter physics. We propose to use this system as a set of interacting quantum bits. We will briefly describe the system and discuss how the qubits can be addressed and manipulated, including interqubit excitation transfer. The working frequency of the proposed quantum computer is ~1GHz. The relaxation rate can be at least 5 orders of magnitude smaller, for low temperatures.

quant-ph↗

arXiv2001

Controlling activated processes

The rates of activated processes, such as escape from a metastable state and nucleation, are exponentially sensitive to an externally applied field. We describe how this applies to modulation by high-frequency fields and illustrate it with experimental observations. The results may lead to selective control of diffusion in periodic potentials, novel control mechanisms for crystal growth, and new separation techniques.

cond-mat.stat-mech↗

arXiv2001

Tunneling decay in a magnetic field

We provide a semiclassical theory of tunneling decay in a magnetic field and a three-dimensional potential of a general form. Because of broken time-reversal symmetry, the standard WKB technique has to be modified. The decay rate is found from the analysis of the set of the particle Hamiltonian trajectories in complex phase space and time. In a magnetic field, the tunneling particle comes out from the barrier with a finite velocity and behind the boundary of the classically allowed region. The exit location is obtained by matching the decaying and outgoing WKB waves at a caustic in complex configuration space. Different branches of the WKB wave function match on the switching surface in real space, where the slope of the wave function sharply changes. The theory is not limited to tunneling from potential wells which are parabolic near the minimum. For parabolic wells, we provide a bounce-type formulation in a magnetic field. The theory is applied to specific models which are relevant to tunneling from correlated two-dimensional electron systems in a magnetic field parallel to the electron layer.

cond-mat.mes-hall↗

arXiv2001

Enhancement of tunneling from a correlated 2D electron system by a many-electron Mossbauer-type recoil in a magnetic field

We consider the effect of electron correlations on tunneling from a 2D electron layer in a magnetic field parallel to the layer. A tunneling electron can exchange its momentum with other electrons, which leads to an exponential increase of the tunneling rate compared to the single-electron approximation. Explicit results are obtained for a Wigner crystal. They provide a qualitative and quantitative explanation of the data on electrons on helium. We also discuss tunneling in semiconductor heterostructures.

cond-mat.mes-hall↗

arXiv2001

Tunneling from a correlated 2D electron system transverse to a magnetic field

We show that, in a magnetic field parallel to the 2D electron layer, strong electron correlations change the rate of tunneling from the layer exponentially. It results in a specific density dependence of the escape rate. The mechanism is a dynamical Mossbauer-type recoil, in which the Hall momentum of the tunneling electron is partly transferred to the whole electron system, depending on the interrelation between the rate of interelectron momentum exchange and the tunneling duration. We also show that, in a certain temperature range, magnetic field can enhance rather than suppress the tunneling rate. The effect is due to the magnetic field induced energy exchange between the in-plane and out-of-plane motion. Magnetic field can also induce switching between intra-well states from which the system tunnels, and a transition from tunneling to thermal activation. Explicit results are obtained for a Wigner crystal. They are in qualitative and quantitative agreement with the relevant experimental data, with no adjustable parameters.

cond-mat.mes-hall↗

arXiv2000

Single electron magneto-conductivity of a nondegenerate 2D electron system in a quantizing magnetic field

We study transport properties of a non-degenerate two-dimensional system of non-interacting electrons in the presence of a quantizing magnetic field and a short-range disorder potential. We show that the low-frequency magnetoconductivity displays a strongly asymmetric peak at a nonzero frequency. The shape of the peak is restored from the calculated 14 spectral moments, the asymptotic form of its high-frequency tail, and the scaling behavior of the conductivity for omega -> 0. We also calculate 10 spectral moments of the cyclotron resonance absorption peak and restore the corresponding (non-singular) frequency dependence using the continuous fraction expansion. Both expansions converge rapidly with increasing number of included moments, and give numerically accurate results throughout the region of interest. We discuss the possibility of experimental observation of the predicted effects for electrons on helium.

cond-mat.str-el↗

arXiv2000

Quantum Computing Using Electrons Floating on Liquid Helium

The system of electrons trapped in vacuum above the liquid helium surface displays the highest mobilities known in condensed matter physics. We provide a brief summary of the experimental and theoretical results obtained for this system. We then show that a quasi-2D set of N > 10^8 electrons in vacuum trapped in 1D hydrogenic levels above a micron-thick helium film can be used as an easily manipulated strongly interacting set of quantum bits. Individual electrons are laterally confined by micron sized metal pads below the helium. Information is stored in the lowest hydrogenic levels. Using electric fields at temperatures of 10 mK, changes in the wave function can be made in nanoseconds. Wave function coherence times are .1 millisecond. The wave function is read out using an inverted dc voltage which releases excited electrons from the surface, or using SETs attached to the metal pads which control the electrons.

quant-ph↗

arXiv2000

Tunneling transverse to a magnetic field, and how it occurs in correlated 2D electron systems

We investigate tunneling decay in a magnetic field. Because of broken time-reversal symmetry, the standard WKB technique does not apply. The decay rate and the outcoming wave packet are found from the analysis of the set of the particle Hamiltonian trajectories and its singularities in complex space. The results are applied to tunneling from a strongly correlated 2D electron system in a magnetic field parallel to the layer. We show in a simple model that electron correlations exponentially strongly affect the tunneling rate.

cond-mat.mes-hall↗

arXiv2000

Dynamics of Activated Escape, and Its Observation in a Semiconductor Laser

We report a direct experimental observation and provide a theory of the distribution of trajectories along which a fluctuating system moves over a potential barrier in escape from a metastable state. The experimental results are obtained for a semiconductor laser with optical feedback. The distribution of paths displays a distinct peak, which shows how the escaping system is most likely to move. We argue that the specific features of this distribution may give an insight into the nature of dropout events in lasers.

cond-mat.stat-mech↗

arXiv2000

Low-frequency peak in the magnetoconductivity of a non-degenerate 2D electron liquid

We study the frequency-dependent magnetoconductivity of a strongly correlated nondegenerate 2D electron system in a quantizing magnetic field. We first restore the single-electron conductivity from calculated 14 spectral moments. It has a maximum for omega ~ gamma (hbar gamma is the disorder-induced width of the Landau level), and scales as a power of omega for omega ->0, with a universal exponent. Even for strong coupling to scatterers, the electron-electron interaction modifies the conductivity for low and high frequencies, and gives rise to a nonzero static conductivity. We analyze the full many-electron conductivity, and discuss the experiment.

cond-mat.mes-hall↗

arXiv1997

Fluctuational phase-flip transitions in parametrically pumped oscillators

We analyze the rates of noise-induced transitions between period-two attractors. The model investigated is an underdamped oscillator parametrically driven by a field at nearly twice the oscillator eigenfrequency. The activation energy of the transitions is analyzed as a function of the frequency detuning and field amplitude scaled by the damping and nonlinearity parameters of the oscillator. The parameter ranges where the system is bi- and tristable are investigated. Explicit results are obtained in the limit of small damping (or strong driving), and near bifurcation points.

physics.optics↗

arXiv1997

Logarithmic susceptibility and optimal control of large fluctuations

We analyze the probabilities of large infrequent fluctuations in systems driven by external fields. In a broad range of the field magnitudes, the logarithm of the fluctuation probability is linear in the field magnitude, and the response can be characterized by a logarithmic susceptibility. This susceptibility is used to analyze optimal control of large fluctuations. For nonadiabatic driving, the activation energies for nucleation and for escape of a Brownian particle display singular behavior as a function of the field shape.

cond-mat.stat-mech↗

arXiv1996

Internal Forces and the Magnetoconductivity of a Nondegenerate 2D Electron Fluid

The forces on individual electrons in an unscreened nondegenerate electron fluid, due to electron density fluctuations, have been calculated using Monte Carlo simulations and determined experimentally over a broad range of the plasma parameter Gamma. The experimental results are obtained from the magnetoconductivity sigma(B) measured for electrons on liquid helium below 1 K for B \leq 8 T. The magnitude and density dependence of sigma(B) are explained by the many-electron theory of magnetotransport. The internal electric fields found from the experiments are in excellent agreement with the simulations.

cond-mat↗

arXiv1993

High Frequency Stochastic Resonance in Periodically Driven Systems

High frequency stochastic resonance (SR) phenomena, associated with fluctuational transitions between coexisting periodic attractors, have been investigated experimentally in an electronic model of a single-well Duffing oscillator bistable in a nearly resonant field of frequency $ω_F$. It is shown that, with increasing noise intensity, the signal/noise ratio (SNR) for a signal due to a weak trial force of frequency $Ω\sim ω_F$ at first decreases, then {\it increases}, and finally decreases again at higher noise intensities: behaviour similar to that observed previously for conventional (low frequency) SR in systems with static bistable potentials. The stochastic enhancement of the SNR of an additional signal at the mirror-reflected frequency $\vert Ω- 2 ω_F \vert$ is also observed, in accordance with theoretical predictions. Relationships with phenomena in nonlinear optics are discussed.

chao-dyn↗