arXiv subjects

Alexander L. Burin

Publications and source records attributed to Alexander L. Burin.

At least 37 records · Page 2Linked to original sources

arXiv2018

Nonuniversality and strongly interacting two-level systems in glasses at low temperatures

Recent experimental results showing untypical nonlinear absorption and marked deviations from well known universality in the low temperature acoustic and dielectric losses in amorphous solids prove the need for improving the understanding of the nature of two-level systems (TLSs) in these materials. Here we suggest the study of TLSs focused on their properties which are nonuniversal. Our theoretical analysis shows that the standard tunneling model and the recently suggested Two-TLS model provide markedly different predictions for the experimental outcome of these studies. Our results may be directly tested in disordered lattices, e.g KBr:CN, where there is ample theoretical support for the validity of the Two-TLS model, as well as in amorphous solids. Verification of our results in the latter will significantly enhance understanding of the nature of TLSs in amorphous solids, and the ability to manipulate them and reduce their destructive effect in various cutting edge applications including superconducting qubits.

cond-mat.dis-nn↗

arXiv2017

Revealing the nonlinear response of a tunneling two-level system ensemble using coupled modes

Atomic sized two-level systems (TLSs) in amorphous dielectrics are known as a major source of loss in superconducting devices. In addition, individual TLS are known to induce large frequency shifts due to strong coupling to the devices. However, in the presence of a broad ensemble of TLSs these shifts are symmetrically canceled out and not observed in a typical single-tone spectroscopy experiment. We introduce a two-tone spectroscopy on the normal modes of a pair of coupled superconducting coplanar waveguide resonators to reveal this effect. Together with an appropriate saturation model this enables us to extract the average single-photon Rabi frequency of dominant TLSs to be $Ω_0/2π\approx 79 $ kHz. At high photon numbers we observe an enhanced frequency shift due to nonlinear kinetic inductance when using the two-tone method and estimate the value of the nonlinear coefficient as $K/2π\approx -1\times 10^{-4}$ Hz/photon. Furthermore, the life-time of each resonance can be controlled (increased) by pumping of the other mode as demonstrated both experimentally and theoretically.

cond-mat.mes-hall↗

arXiv2017

Comment on "Many-body localization in Ising models with random long-range interactions"

This comment is dedicated to the investigation of many-body localization in a quantum Ising model with long-range power law interactions, $r^{-α}$, relevant for a variety of systems ranging from electrons in Anderson insulators to spin excitations in chains of cold atoms. It has been earlier argued [1, 2] that this model obeys the dimensional constraint suggesting the delocalization of all finite temperature states in thermodynamic limit for $α\leq 2d$ in a $d$-dimensional system. This expectation conflicts with the recent numerical studies of the specific interacting spin model in Ref. [3]. To resolve this controversy we reexamine the model of Ref. [3] and demonstrate that the infinite temperature states there obey the dimensional constraint. The earlier developed scaling theory for the critical system size required for delocalization [2] is extended to small exponents $0 \leq α\leq d$. Disagreements between two works are explained by the non-standard selection of investigated states in the ordered phase and misinterpretation of the localization-delocalization transition in Ref. [3].

cond-mat.dis-nn↗

arXiv2017

Localization and chaos in a spin glass model with random fields: Mapping to the localization problem in a Bethe lattice with a correlated disorder

The analytical solution of a many-body localization problem in a quantum Sherrington-Kirkpatrick spin glass model in a random longitudinal field is proposed matching the problem with a model of Anderson localization in a Bethe lattice. The localization transition is dramatically sensitive to the relationship between interspin interaction and random field revealing different regimes in which the interaction can either suppress or enhance the delocalization. The localization is enhanced by decreasing the temperature and the localization transition shows a remarkable universality in a spin glass phase. The observed trends should be qualitatively relevant for other systems showing many-body localization.

cond-mat.dis-nn↗

arXiv2017

Analytical theory of many-body localization in the presence of periodic drive

Many-body localization transition in a periodically driven quantum system is investigated using a solution of a matching Bethe lattice problem for Floquet states of a quantum random energy model with a generalization to more realistic settings. It turns out that an external periodic field can both suppress and enhance localization depending on field amplitude and frequency which leads to three distinguishable regimes of field enhanced, controlled and suppressed delocalization. The results can be verified experimentally in systems of cold atoms and/or interacting spin defects in semiconductors.

cond-mat.dis-nn↗

arXiv2016

Exact solution for low energy quantum anharmonic vibrations in a long polymer chain

We propose the algorithm for determining vibrational quantum eigenstates of periodic linear chain of atoms coupled by harmonic and third order anharmonic interactions (Fermi-Ulam-Pasta $α$ problem) in the long wavelength limit within the resonant approach. Eigenstates can be encoded by the sequence of integer numbers determining their energies and wavefunctions. Using these eigenstates we described a single phonon state time evolution showing coherent oscillations. The applications of theory to vibrational energy transport and quantum informatics are discussed.

cond-mat.dis-nn↗

arXiv2016

Projected dipole moments of individual two-level defects extracted using circuit quantum electrodynamics

Material-based two-level systems (TLSs), appearing as defects in low-temperature devices including superconducting qubits and photon detectors, are difficult to characterize. In this study we apply a uniform dc-electric field across a film to tune the energies of TLSs within. The film is embedded in a superconducting resonator such that it forms a circuit quantum electrodynamical (cQED) system. The energy of individual TLSs is observed as a function of the known tuning field. By studying TLSs for which we can determine the tunneling energy, the actual $p_z$, dipole moments projected along the uniform field direction, are individually obtained. A distribution is created with 60 $p_z$. We describe the distribution using a model with two dipole moment magnitudes, and a fit yields the corresponding values $p=p_1= 2.8\pm 0.2$ Debye and $p=p_2=8.3\pm0.4$ Debye. For a strong-coupled TLS the vacuum-Rabi splitting can be obtained with $p_z$ and tunneling energy. This allows a measurement of the circuit's zero-point electric field fluctuations, in a method that does not need the electric-field volume.

cond-mat.supr-con↗

arXiv2016

Electronic torsional sound in linear atomic chains: chemical energy transport at 1000 km/s

We investigate entirely electronic torsional vibrational modes in linear cumulene chains. The carbon nuclei of a cumulene are positioned along the primary axis so they can participate only in transverse and longitudinal motions. However, the interatomic electronic clouds behave as a torsion spring with remarkable torsional stiffness. The collective dynamics of these clouds can be described in terms of electronic vibrational quanta, which we name torsitons. It is shown that the group velocity of the wavepacket of torsitons is much higher than the typical speed of sound, because of the small mass of participating electrons compared to the atomic mass. For the same reason the maximum energy of the torsitons in cumulenes is as high as a few electronvolts, while the minimum possible energy is evaluated as a few hundred wavenumbers and this minimum is associated with asymmetry of zero point atomic vibrations. Molecular systems for experimental evaluation of the predictions are proposed.

physics.chem-ph↗

arXiv2015

Localization in a random $x-y$ model with the long-range interaction: Intermediate case between single particle and many-body problems

Many-body localization in an $XY$ model with a long-range interaction is investigated. We show that in the regime of a high strength of disordering compared to the interaction an off-resonant flip-flop spin-spin interaction (hopping) generates the effective Ising interactions of spins in the third order of perturbation theory in a hopping. The combination of hopping and induced Ising interactions for the power law distance dependent hopping $V(R) \propto R^{-α}$ always leads to the localization breakdown in a thermodynamic limit of an infinite system at $α< 3d/2$ where $d$ is a system dimension. The delocalization takes place due to the induced Ising interactions $U(R) \propto R^{-2α}$ of "extended" resonant pairs. This prediction is consistent with the numerical finite size scaling in one-dimensional systems. Many-body localization in $XY$ model is more stable with respect to the long-range interaction compared to a many-body problem with similar Ising and Heisenberg interactions requiring $α\geq 2d$ which makes the practical implementations of this model more attractive for quantum information applications. The full summary of dimension constraints and localization threshold size dependencies for many-body localization in the case of combined Ising and hopping interactions is obtained using this and previous work and it is the subject for the future experimental verification using cold atomic systems.

cond-mat.dis-nn↗

arXiv2015

Cavity quantum electrodynamics using a near-resonance two-level system: emergence of the Glauber state

Random tunneling two-level systems (TLSs) in dielectrics have been of interest recently because they adversely affect the performance of superconducting qubits. The coupling of TLSs to qubits has allowed individual TLS characterization, which has previously been limited to TLSs within (thin) Josephson tunneling barriers made from aluminum oxide. Here we report on the measurement of an individual TLS within the capacitor of a lumped-element LC microwave resonator, which forms a cavity quantum electrodynamics (CQED) system and allows for individual TLS characterization in a different structure and material than demonstrated with qubits. Due to the reduced volume of the dielectric (80 $μ$m$^{3}$), even with a moderate dielectric thickness (250 nm), we achieve the strong coupling regime as evidenced by the vacuum Rabi splitting observed in the cavity spectrum. A TLS with a coherence time of 3.2 $μ$s was observed in a film of silicon nitride as analyzed with a Jaynes-Cummings spectral model, which is larger than seen from superconducting qubits. As the drive power is increased, we observe an unusual but explicable set of continuous and discrete crossovers from the vacuum Rabi split transitions to the Glauber (coherent) state.

cond-mat.supr-con↗

arXiv2015

Low temperature 1/f noise in microwave dielectric constant of amorphous dielectrics in Josephson qubits

The accurate analytical solution for the low temperature $1/f$ noise in a microwave dielectric constant of amorphous films containing tunneling two-level systems (TLSs) is derived within the standard tunneling model including the weak dipolar or elastic TLS-TLS interactions. The results are consistent with the recent experimental investigations of $1/f$ noise in Josephson junction qubits including the power law increase of the noise amplitude with decreasing temperature at low temperatures $T<0.1$K. The long time correlations needed for $1/f$ noise are provided by the logarithmic broadening of TLS absorption resonances with time due to their interaction with neighboring TLSs. The noise behavior at higher temperatures $T>0.1$K and its possible sensitivity to quasi-particle excitations are discussed.

cond-mat.dis-nn↗

arXiv2015

Many-Body Delocalization in Strongly Disordered System with Long-Range Interactions: Finite Size Scaling

Many-body localization in a disordered system of interacting spins coupled by the long-range interaction $1/R^α$ is investigated combining analytical theory considering resonant interactions and a finite size scaling of exact numerical solutions with a number of spins $N$. The numerical results for a one-dimensional system are consistent with the general expectations of analytical theory for $d$-dimensional system including the absence of localization in the infinite system at $α<2d$ and a universal scaling of a critical energy disordering $W_{c} \propto N^{\frac{2d-α}{d}}$. %The finite size effect on the interaction stimulated delocalization of energy in the ensemble of interacting two level systems in amorphous solids at low temperature is discussed.

cond-mat.dis-nn↗

arXiv2014

Many-Body Delocalization in Strongly Disordered System with Long-Range Interactions: Finite Size Scaling

The localization in a disordered system of $N$ interacting spins coupled by the long-range anisotropic interaction $1/R^α$ is investigated using a finite size scaling in a $d=1$ -dimensional system for $N=8, 10, 12, 14$. The results supports the absence of localization in the infinite system at $α<2d$ and a scaling of a critical energy disordering $W_{c} \propto N^{2d-α}$ in agreement with the analytical theory suggesting the energy delocalization in the subset of interacting resonant pairs of spins as a precursor of the many-body delocalization.The spin relaxation rate $k$ dependence on disordering $k \propto W^{-2}$ has been revealed in the practically interesting case $α=d$. This relaxation mechanism can be responsible for the anomalous relaxation of quantum two level systems in amorphous solids.

cond-mat.dis-nn↗

arXiv2014

Fast transport and relaxation of vibrational energy in polymer chains

We investigate ballistic vibrational energy transport through optical phonon band in oligomeric chains in the presence of decoherence. An exact solution is obtained for the excitation density in the space-time representation in the continuous limit and this solution is used to characterize the energy transport time and intensity. Three transport mechanisms are identified such as ballistic, diffusive and directed diffusive regimes, occurring at different distances and time ranges. The crossover between the two diffusive regimes is continuous, while the switch between the ballistic and diffusive mechanisms occurs in discontinuous manner in accord with the recent experimental data on energy transport in perfluoroalkanes.

physics.chem-ph↗

arXiv2013

Universal dielectric loss in amorphous solids from simultaneous bias and microwave field

We derive the ac dielectric loss in glasses due to resonant processes created by two-level systems and a swept electric field bias. It is shown that at sufficiently large ac fields and bias sweep rates the nonequilibrium loss tangent created by the two fields approaches a universal maximum determined by the bare linear dielectric permittivity. In addition this nonequilibrium loss tangent is derived for a range of bias sweep rates and ac amplitudes and show that the loss tangent creates a predicted loss function that can be understood in a Landau-Zener theory and which can be used to extract the TLS density, dipole moment, and relaxation rate.

cond-mat.dis-nn↗

arXiv2012

Low temperature dipolar echo in amorphous dielectrics: Significance of relaxation and decoherence free two level systems

The nature of dielectric echoes in amorphous solids at low temperatures is investigated. It is shown that at long delay times the echo amplitude is determined by a small subset of two level systems (TLS) having negligible relaxation and decoherence because of their weak coupling to phonons. The echo decay can then be described approximately by power law time dependencies with different powers at times longer and shorter than the typical TLS relaxation time. The theory is applied to recent measurements of two and three pulse dipolar echo in borosilicate glass BK7 and provides a perfect data fit in the broad time and temperature ranges under the assumption that there exist two TLS relaxation mechanisms due to TLS-phonons and TLS-TLS interaction. This interpretation is consistent with the previous experimental and theoretical investigations. Further experiments verifying the theory predictions are suggested.

cond-mat.dis-nn↗

arXiv2010

Fluctuator model of memory dip in hopping insulators

We show that the non-equilibrium dynamic in two-dimensional electron glasses close to metal-dielectric transition is dramatically sensitive to electric fields confinement inside the sample, which leads to a nearly thermally activated conductance behavior and a strong non-equilibrium conductance response to the gate voltage, i. e. memory dip in a field dependence of conductance. Theory accounts qualitatively and quantitatively for the universal temperature and field dependencies of memory dip.

cond-mat.dis-nn↗

arXiv2008

Localization of positive charge in DNA induced by its interaction with environment

Microscopic mechanisms of positive charge transfer in DNA remain unclear. A quantum state of electron hole in DNA is determined by the competition of the pi-stacking interaction $b$ sharing a charge between different base pairs and the interaction $λ$ with the local environment which attempts to trap charge. To determine which interaction dominates we investigated charge quantum states in various $(GC)_{n}$ sequences choosing DNA parameters satisfying experimental data for the balance of charge transfer rates $G^{+} \leftrightarrow G_{n}^{+}$, $n=2,3$ \cite{FredMain}. We show that experimental data can be consistent with theory only assuming $b\ll λ$ meaning that charge is typically localized within the single $G$ site. Consequently any DNA sequence including the one consisting of identical base pairs behaves more like an insulating material then a molecular conductor. Our theory can be verified experimentally, for instance measuring balance of charge transfer reactions $G^{+} \leftrightarrow G_{n}^{+}$, $n \geq 4$ and comparing the experimental results with our predictions.

cond-mat.soft↗