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Vladyslav Kozii - One of the best experts on this subject based on the ideXlab platform.
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dmft reveals the non hermitian topology and fermi arcs in heavy fermion systems
Physical Review Letters, 2020Co-Authors: Yuki Nagai, Hiroki Isobe, Vladyslav KoziiAbstract:When a strongly correlated system supports well-defined Quasiparticles, it allows for an elegant one-body effective description within the non-Hermitian topological theory. While the microscopic many-body Hamiltonian of a closed system remains Hermitian, the one-body Quasiparticle Hamiltonian is non-Hermitian due to the finite Quasiparticle lifetime. We use such a non-Hermitian description in the heavy-fermion two-dimensional systems with the momentum-dependent hybridization to reveal a fascinating phenomenon which can be directly probed by the spectroscopic measurements, the bulk "Fermi arcs." Starting from a simple two-band model, we first combine the phenomenological approach with the perturbation theory to show the existence of the Fermi arcs and reveal their connection to the topological exceptional points, special points in the Brillouin zone where the Hamiltonian is nondiagonalizable. The appearance of such points necessarily requires that the electrons belonging to different orbitals have different lifetimes. This requirement is naturally satisfied in the heavy-fermion systems, where the itinerant c electrons experience much weaker interaction than the localized f electrons. We then utilize the dynamical mean field theory to numerically calculate the spectral function and confirm our findings. We show that the concept of the exceptional points in the non-Hermitian Quasiparticle Hamiltonians is a powerful tool for predicting new phenomena in strongly correlated electron systems.
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dmft reveals the non hermitian topology in heavy fermion systems
arXiv: Strongly Correlated Electrons, 2020Co-Authors: Yuki Nagai, Hiroki Isobe, Vladyslav KoziiAbstract:We find that heavy fermion systems can have bulk "Fermi arcs", with the use of the non-Hermitian topological theory. In an interacting electron system, the microscopic many-body Hamiltonian is Hermitian, but the one-body Quasiparticle Hamiltonian is non-Hermitian due to the finite Quasiparticle lifetime. We focus on heavy electron systems as a stage of finite lifetime Quasiparticles with two lifetimes, since Quasiparticle lifetimes for f-electrons and c-electrons should be different. Two lifetimes induce exceptional points (EPs) of the non-Hermitian Quasiparticle Hamiltonian matrix in momentum space. The line connecting between two EPs characterizes the bulk Fermi arcs. With the use of the dynamical mean field theory (DMFT) calculation, we confirm our statement in Kondo insulators with a momentum-dependent hybridization in two-dimensions. We show that the concept of the EPs in the non-Hermitian Quasiparticle Hamiltonian is one of powerful tools to predict new phenomena in strongly correlated electron systems.
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non hermitian topological theory of finite lifetime Quasiparticles prediction of bulk fermi arc due to exceptional point
Bulletin of the American Physical Society, 2018Co-Authors: Vladyslav KoziiAbstract:Author(s): Kozii, Vladyslav; Fu, Liang | Abstract: We introduce a topological theory to study Quasiparticles in interacting and/or disordered many-body systems, which have a finite lifetime due to inelastic and/or elastic scattering. The one-body Quasiparticle Hamiltonian includes both the Bloch Hamiltonian of band theory and the self-energy due to interactions, which is non-Hermitian when Quasiparticle lifetime is finite. We study the topology of non-Hermitian Quasiparticle Hamiltonians in momentum space, whose energy spectrum is complex. The interplay of band structure and Quasiparticle lifetime is found to have remarkable consequences in zero- and small-gap systems. In particular, we predict the existence of topological exceptional point and bulk Fermi arc in Dirac materials with two distinct Quasiparticle lifetimes.
Gianluigi Catelani - One of the best experts on this subject based on the ideXlab platform.
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measurement and control of Quasiparticle dynamics in a superconducting qubit
Nature Communications, 2014Co-Authors: Chen Wang, U Vool, T Brecht, Yvonne Y Gao, M H Devoret, Luigi Frunzio, Ioan M Pop, Christopher Axline, Reinier W Heeres, Gianluigi CatelaniAbstract:Superconducting circuits have attracted growing interest in recent years as a promising candidate for fault-tolerant quantum information processing. Extensive efforts have always been taken to completely shield these circuits from external magnetic fields to protect the integrity of the superconductivity. Here we show vortices can improve the performance of superconducting qubits by reducing the lifetimes of detrimental single-electron-like excitations known as Quasiparticles. Using a contactless injection technique with unprecedented dynamic range, we quantitatively distinguish between recombination and trapping mechanisms in controlling the dynamics of residual Quasiparticle, and show quantized changes in Quasiparticle trapping rate because of individual vortices. These results highlight the prominent role of Quasiparticle trapping in future development of superconducting qubits, and provide a powerful characterization tool along the way.
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non poissonian quantum jumps of a fluxonium qubit due to Quasiparticle excitations
Physical Review Letters, 2014Co-Authors: U Vool, Ioan Pop, K Sliwa, B Abdo, Chen Wang, T Brecht, Yvonne Y Gao, S Shankar, Michael Hatridge, Gianluigi CatelaniAbstract:(Received 27 May 2014; revised manuscript received 30 September 2014; published 8 December 2014) As the energy relaxation time of superconducting qubits steadily improves, nonequilibrium Quasiparticle excitations above the superconducting gap emerge as an increasingly relevant limit for qubit coherence. We measure fluctuations in the number of Quasiparticle excitations by continuously monitoring the spontaneous quantum jumps between the states of a fluxonium qubit, in conditions where relaxation is dominated by Quasiparticle loss. Resolution on the scale of a single Quasiparticle is obtained by performing quantum nondemolition projective measurements within a time interval much shorter than T1, using a quantum-limited amplifier (Josephson parametric converter). The quantum jump statistics switches between the expected Poisson distribution and a non-Poissonian one, indicating large relative fluctuations in the Quasiparticle population, on time scales varying from seconds to hours. This dynamics can be modified controllably by injecting Quasiparticles or by seeding Quasiparticle-trapping vortices by cooling down in a magnetic field.
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coherent suppression of electromagnetic dissipation due to superconducting Quasiparticles
Nature, 2014Co-Authors: Ioan M Pop, L I Glazman, Gianluigi Catelani, R J Schoelkopf, K Geerlings, M H DevoretAbstract:The long-predicted suppression of Quasiparticle dissipation in a Josephson junction when the phase difference across the junction is π is inferred from a sharp maximum in the energy relaxation time of a superconducting artificial atom. Josephson junctions, which consist of two superconductors connected by a weak link, have a central role in quantum electronic applications, such as in sensitive magnetic field detectors, high-speed processing and quantum information networks. However, a fundamental prediction concerning the Josephson effect has not yet been confirmed. It is known that the current flowing through a Josephson junction is made up from superconducting Cooper pairs as well as excitations called Quasiparticles, which contribute in a few different ways. One contribution causes dissipation but can in theory be suppressed by tuning the phase difference between the superconductors. This has been achieved experimentally. Ioan Pop et al. have made a qubit comprising a Josephson junction. The energy relaxation time of this qubit increases by almost two orders of magnitude owing to the suppression of Quasiparticle dissipation. This finding confirms the existence of a fundamental quantum phenomenon predicted over 50 years ago. Owing to the low-loss propagation of electromagnetic signals in superconductors, Josephson junctions constitute ideal building blocks for quantum memories, amplifiers, detectors and high-speed processing units, operating over a wide band of microwave frequencies. Nevertheless, although transport in superconducting wires is perfectly lossless for direct current, transport of radio-frequency signals can be dissipative in the presence of Quasiparticle excitations above the superconducting gap1. Moreover, the exact mechanism of this dissipation in Josephson junctions has never been fully resolved experimentally. In particular, Josephson’s key theoretical prediction that Quasiparticle dissipation should vanish in transport through a junction when the phase difference across the junction is π (ref. 2) has never been observed3. This subtle effect can be understood as resulting from the destructive interference of two separate dissipative channels involving electron-like and hole-like Quasiparticles. Here we report the experimental observation of this quantum coherent suppression of Quasiparticle dissipation across a Josephson junction. As the average phase bias across the junction is swept through π, we measure an increase of more than one order of magnitude in the energy relaxation time of a superconducting artificial atom. This striking suppression of dissipation, despite the presence of lossy Quasiparticle excitations above the superconducting gap, provides a powerful tool for minimizing decoherence in quantum electronic systems and could be directly exploited in quantum information experiments with superconducting quantum bits.
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measurements of Quasiparticle tunneling dynamics in a band gap engineered transmon qubit
Physical Review Letters, 2012Co-Authors: L Dicarlo, Matthew Reed, Gianluigi Catelani, Lev S Bishop, David Schuster, Blake JohnsonAbstract:We have engineered the band gap profile of transmon qubits by combining oxygen-doped Al for tunnel junction electrodes and clean Al as Quasiparticle traps to investigate energy relaxation due to Quasiparticle tunneling. The relaxation time T1 of the qubits is shown to be insensitive to this band gap engineering. Operating at relatively low-EJ/EC makes the transmon transition frequency distinctly dependent on the charge parity, allowing us to detect the Quasiparticles tunneling across the qubit junction. Quasiparticle kinetics have been studied by monitoring the frequency switching due to even-odd parity change in real time. It shows the switching time is faster than 10???s, indicating Quasiparticle-induced relaxation has to be reduced to achieve T1 much longer than 100???s.
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relaxation and frequency shifts induced by Quasiparticles in superconducting qubits
Physical Review B, 2011Co-Authors: Gianluigi Catelani, R J Schoelkopf, M H Devoret, L I GlazmanAbstract:As low-loss nonlinear elements, Josephson junctions are the building blocks of superconducting qubits. The interaction of the qubit degree of freedom with the Quasiparticles tunneling through the junction represents an intrinsic relaxation mechanism. We develop a general theory for the qubit decay rate induced by Quasiparticles, and we study its dependence on the magnetic flux used to tune the qubit properties in devices such as the phase and flux qubits, the split transmon, and the fluxonium. Our estimates for the decay rate apply to both thermal equilibrium and nonequilibrium Quasiparticles. We propose measuring the rate in a split transmon to obtain information on the possible nonequilibrium Quasiparticle distribution. We also derive expressions for the shift in qubit frequency in the presence of Quasiparticles.
L Dicarlo - One of the best experts on this subject based on the ideXlab platform.
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millisecond charge parity fluctuations and induced decoherence in a superconducting transmon qubit
Nature Communications, 2013Co-Authors: Diego Riste, C C Bultink, M J Tiggelman, R N Schouten, K W Lehnert, L DicarloAbstract:The tunnelling of Quasiparticles across Josephson junctions in superconducting quantum circuits is an intrinsic decoherence mechanism for qubit degrees of freedom. Understanding the limits imposed by Quasiparticle tunnelling on qubit relaxation and dephasing is of theoretical and experimental interest, particularly as improved understanding of extrinsic mechanisms has allowed crossing the 100 microsecond mark in transmon-type charge qubits. Here, by integrating recent developments in high-fidelity qubit readout and feedback control in circuit quantum electrodynamics, we transform a state-of-the-art transmon into its own real-time charge-parity detector. We directly measure the tunnelling of Quasiparticles across the single junction and isolate the contribution of this tunnelling to qubit relaxation and dephasing, without reliance on theory. The millisecond timescales measured demonstrate that Quasiparticle tunnelling does not presently bottleneck transmon qubit coherence, leaving room for yet another order of magnitude increase.
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measurements of Quasiparticle tunneling dynamics in a band gap engineered transmon qubit
Physical Review Letters, 2012Co-Authors: L Dicarlo, Matthew Reed, Gianluigi Catelani, Lev S Bishop, David Schuster, Blake JohnsonAbstract:We have engineered the band gap profile of transmon qubits by combining oxygen-doped Al for tunnel junction electrodes and clean Al as Quasiparticle traps to investigate energy relaxation due to Quasiparticle tunneling. The relaxation time T1 of the qubits is shown to be insensitive to this band gap engineering. Operating at relatively low-EJ/EC makes the transmon transition frequency distinctly dependent on the charge parity, allowing us to detect the Quasiparticles tunneling across the qubit junction. Quasiparticle kinetics have been studied by monitoring the frequency switching due to even-odd parity change in real time. It shows the switching time is faster than 10???s, indicating Quasiparticle-induced relaxation has to be reduced to achieve T1 much longer than 100???s.
Alexey V Gorshkov - One of the best experts on this subject based on the ideXlab platform.
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confined Quasiparticle dynamics in long range interacting quantum spin chains
Physical Review Letters, 2019Co-Authors: Fangli Liu, Rex Lundgren, Paraj Titum, Guido Pagano, J Zhang, C Monroe, Alexey V GorshkovAbstract:We study the Quasiparticle excitation and quench dynamics of the one-dimensional transverse-field Ising model with power-law (1/r^{α}) interactions. We find that long-range interactions give rise to a confining potential, which couples pairs of domain walls (kinks) into bound Quasiparticles, analogous to mesonic states in high-energy physics. We show that these Quasiparticles have signatures in the dynamics of order parameters following a global quench, and the Fourier spectrum of these order parameters can be exploited as a direct probe of the masses of the confined Quasiparticles. We introduce a two-kink model to qualitatively explain the phenomenon of long-range-interaction-induced confinement and to quantitatively predict the masses of the bound Quasiparticles. Furthermore, we illustrate that these Quasiparticle states can lead to slow thermalization of one-point observables for certain initial states. Our work is readily applicable to current trapped-ion experiments.
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confined Quasiparticle dynamics in long range interacting quantum spin chains
Physical Review Letters, 2019Co-Authors: Fangli Liu, Rex Lundgren, Paraj Titum, Guido Pagano, J Zhang, C Monroe, Alexey V GorshkovAbstract:We study the Quasiparticle excitation and quench dynamics of the one-dimensional transverse-field Ising model with power-law ($1/{r}^{\ensuremath{\alpha}}$) interactions. We find that long-range interactions give rise to a confining potential, which couples pairs of domain walls (kinks) into bound Quasiparticles, analogous to mesonic states in high-energy physics. We show that these Quasiparticles have signatures in the dynamics of order parameters following a global quench, and the Fourier spectrum of these order parameters can be exploited as a direct probe of the masses of the confined Quasiparticles. We introduce a two-kink model to qualitatively explain the phenomenon of long-range-interaction-induced confinement and to quantitatively predict the masses of the bound Quasiparticles. Furthermore, we illustrate that these Quasiparticle states can lead to slow thermalization of one-point observables for certain initial states. Our work is readily applicable to current trapped-ion experiments.
J P Pekola - One of the best experts on this subject based on the ideXlab platform.
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probing Quasiparticle excitations in a hybrid single electron transistor
Applied Physics Letters, 2012Co-Authors: Helena S Knowles, V F Maisi, J P PekolaAbstract:We investigate the behavior of Quasiparticles in a hybrid electron turnstile with the aim of improving its performance as a metrological current source. The device is used to directly probe the density of Quasiparticles and monitor their relaxation into normal metal traps. We compare different trap geometries and reach Quasiparticle densities below 3 μm−3 for pumping frequencies of 20 MHz. Our data show that Quasiparticles are excited both by the device operation itself and by the electromagnetic environment of the sample. Our observations can be modelled on a quantitative level with a sequential tunneling model and a simple diffusion equation.
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vanishing Quasiparticle density in a hybrid al cu al single electron transistor
Physical Review B, 2012Co-Authors: Ollipentti Saira, A Kemppinen, V F Maisi, J P PekolaAbstract:The achievable fidelity of many nanoelectronic devices based on superconducting aluminum is limited by either the density of residual nonequilibrium Quasiparticles ${n}_{\mathrm{qp}}$ or the density of Quasiparticle states in the gap, characterized by Dynes parameter $\ensuremath{\gamma}$. We infer upper bounds ${n}_{\mathrm{qp}}l0.033\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}{\mathrm{m}}^{\ensuremath{-}3}$ and $\ensuremath{\gamma}l1.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$ from transport measurements performed on Al/Cu/Al single-electron transistors, improving previous results by an order of magnitude. Owing to efficient microwave shielding and Quasiparticle relaxation, a typical number of Quasiparticles in the superconducting leads is zero.
