Recursos de colección

Caltech Authors (142.336 recursos)

Repository of works by Caltech published authors.

Group = IQIM

Mostrando recursos 1 - 20 de 515

  1. Quasiparticle explanation of the weak-thermalization regime under quench in a nonintegrable quantum spin chain

    Lin, Cheng-Ju; Motrunich, Olexei I.
    The eigenstate thermalization hypothesis provides one picture of thermalization in a quantum system by looking at individual eigenstates. However, it is also important to consider how local observables reach equilibrium values dynamically. Quench protocol is one of the settings to study such questions. A recent numerical study [Bañuls, Cirac, and Hastings, Phys. Rev. Lett. 106, 050405 (2007)] of a nonintegrable quantum Ising model with longitudinal field under such a quench setting found different behaviors for different initial quantum states. One particular case called the “weak-thermalization” regime showed apparently persistent oscillations of some observables. Here we provide an explanation of such...

  2. Nonlocal Coulomb drag in Weyl semimetals

    Baum, Yuval; Stern, Ady
    Nonlocality is one of the most striking signatures of the topological nature of Weyl semimetals. We propose to probe the nonlocality in these materials via a measurement of a magnetic-field-dependent Coulomb drag between two sheets of graphene which are separated by a three-dimensional slab of Weyl semimetal. We predict a mechanism of Coulomb drag, based on cyclotron orbits that are split between opposite surfaces of the semimetal. In the absence of impurity scattering between different Weyl nodes, this mechanism does not decay with the thickness of the semimetal.

  3. Partial breakdown of quantum thermalization in a Hubbard-like model

    Garrison, James R.; Mishmash, Ryan V.; Fisher, Matthew P. A.
    We study the possible breakdown of quantum thermalization in a model of itinerant electrons on a one-dimensional chain without disorder, with both spin and charge degrees of freedom. The eigenstates of this model exhibit peculiar properties in the entanglement entropy, the apparent scaling of which is modified from a “volume law” to an “area law” after performing a partial, site-wise measurement on the system. These properties and others suggest that this model realizes a new, nonthermal phase of matter, known as a quantum disentangled liquid (QDL). The putative existence of this phase has striking implications for the foundations of quantum...

  4. Twisted gauge theories in 3D Walker-Wang models

    Wang, Zitao; Chen, Xie
    Three dimensional gauge theories with a discrete gauge group can emerge from spin models as a gapped topological phase with fractional point excitations (gauge charge) and loop excitations (gauge flux). It is known that 3D gauge theories can be "twisted", in the sense that the gauge flux loops can have nontrivial braiding statistics among themselves and such twisted gauge theories are realized in models discovered by Dijkgraaf and Witten. A different framework to systematically construct three dimensional topological phases was proposed by Walker and Wang and a series of examples have been studied. Can the Walker Wang construction be used...

  5. Uniform Additivity in Classical and Quantum Information

    Cross, Andrew; Li, Ke; Smith, Graeme
    Information theory quantifies the optimal rates of resource interconversions, usually in terms of entropies. However, nonadditivity often makes evaluating entropic formulas intractable. In a few auspicious cases, additivity allows a full characterization of optimal rates. We study uniform additivity of formulas, which is easily evaluated and captures all known additive quantum formulas. Our complete characterization of uniform additivity exposes an intriguing new additive quantity and identifies a remarkable coincidence—the classical and quantum uniformly additive functions with one auxiliary variable are identical.

  6. Spectrum estimation of density operators with alkaline-earth atoms

    Beverland, Michael E.; Haah, Jeongwan; Alagic, Gorjan; Campbell, Gretchen K.; Rey, Ana Maria; Gorshkov, Alexey V.
    We show that Ramsey spectroscopy of fermionic alkaline-earth atoms in a square-well trap provides an efficient and accurate estimate for the eigenspectrum of a density matrix whose n copies are stored in the nuclear spins of n such atoms. This spectrum estimation is enabled by the high symmetry of the interaction Hamiltonian, dictated, in turn, by the decoupling of the nuclear spin from the electrons and by the shape of the square-well trap. Practical performance of this procedure and its potential applications to quantum computing, quantum simulation, and time-keeping with alkaline-earth atoms are discussed.

  7. A charge density wave-like instability in a doped spin-orbit assisted weak Mott insulator

    Chu, H.; Zhao, L.; de la Torre, A.; Hogan, T.; Wilson, S. D.; Hsieh, D.
    Layered perovskite iridates realize a rare class of Mott insulators that are predicted to be strongly spin–orbit coupled analogues of the parent state of cuprate high-temperature superconductors. Recent discoveries of pseudogap, magnetic multipolar ordered6 and possible d-wave superconducting phases in doped Sr_2IrO_4 have reinforced this analogy among the single layer variants. However, unlike the bilayer cuprates, no electronic instabilities have been reported in the doped bilayer iridate Sr_3Ir_2O_7. Here we show that Sr_3Ir_2O_7 realizes a weak Mott state with no cuprate analogue by using ultrafast time-resolved optical reflectivity to uncover an intimate connection between its insulating gap and antiferromagnetism. However,...

  8. Interfacing broadband photonic qubits to on-chip cavity-protected rare-earth ensembles

    Zhong, Tian; Kindem, Jonathan M.; Rochman, Jake; Faraon, Andrei
    Ensembles of solid-state optical emitters enable broadband quantum storage and transduction of photonic qubits, with applications in high-rate quantum networks for secure communications and interconnecting future quantum computers. To transfer quantum states using ensembles, rephasing techniques are used to mitigate fast decoherence resulting from inhomogeneous broadening, but these techniques generally limit the bandwidth, efficiency and active times of the quantum interface. Here, we use a dense ensemble of neodymium rare-earth ions strongly coupled to a nanophotonic resonator to demonstrate a significant cavity protection effect at the single-photon level—a technique to suppress ensemble decoherence due to inhomogeneous broadening. The protected Rabi...

  9. Photocurrents in Weyl semimetals

    Chan, Ching-Kit; Lindner, Netanel H.; Refael, Gil; Lee, Patrick A.
    The generation of photocurrent in an ideal two-dimensional Dirac spectrum is symmetry forbidden. In sharp contrast, we show that three-dimensional Weyl semimetals can generically support significant photocurrents due to the combination of inversion symmetry breaking and finite tilts of the Weyl spectra. Symmetry properties, chirality relations, and various dependencies of this photovoltaic effect on the system and the light source are explored in detail. Our results suggest that noncentrosymmetric Weyl materials can be advantageously applied to room temperature detections of mid- and far-infrared radiations.

  10. Coherent ultra-violet to near-infrared generation in silica ridge waveguides

    Oh, Dong Yoon; Yang, Ki Youl; Fredrick, Connor; Ycas, Gabriel; Diddams, Scott A.; Vahala, Kerry J.
    Short duration, intense pulses of light can experience dramatic spectral broadening when propagating through lengths of optical fibre. This continuum generation process is caused by a combination of nonlinear optical effects including the formation of dispersive waves. Optical analogues of Cherenkov radiation, these waves allow a pulse to radiate power into a distant spectral region. In this work, efficient and coherent dispersive wave generation of visible to ultraviolet light is demonstrated in silica waveguides on a silicon chip. Unlike fibre broadeners, the arrays provide a wide range of emission wavelength choices on a single, compact chip. This new capability is...

  11. Diamond optomechanical crystals

    Burek, Michael J.; Cohen, Justin D.; Meenehan, Seán M.; El-Sawah, Nayera; Chia, Cleaven; Ruelle, Thibaud; Meesala, Srujan; Rochman, Jake; Atikian, Haig A.; Markham, Matthew; Twitchen, Daniel J.; Lukin, Mikhail D.; Painter, Oskar; Lončar, Marko
    Cavity-optomechanical systems realized in single-crystal diamond are poised to benefit from its extraordinary material properties, including low mechanical dissipation and a wide optical transparency window. Diamond is also rich in optically active defects, such as the nitrogen-vacancy (NV) and silicon-vacancy (SiV) centers, which behave as atom-like systems in the solid state. Predictions and observations of coherent coupling of the NV electronic spin to phonons via lattice strain have motivated the development of diamond nanomechanical devices aimed at the realization of hybrid quantum systems in which phonons provide an interface with diamond spins. In this work, we demonstrate diamond optomechanical crystals...

  12. Rescuing complementarity with little drama

    Bao, Ning; Bouland, Adam; Chatwin-Davies, Aidan; Pollack, Jason; Yuen, Henry
    The AMPS paradox challenges black hole complementarity by apparently constructing a way for an observer to bring information from the outside of the black hole into its interior if there is no drama at its horizon, making manifest a violation of monogamy of entanglement. We propose a new resolution to the paradox: this violation cannot be explicitly checked by an infalling observer in the finite proper time they have to live after crossing the horizon. Our resolution depends on a weak relaxation of the no-drama condition (we call it “little-drama”) which is the “complementarity dual” of scrambling of information on...

  13. Real-space mean-field theory of a spin-1 Bose gas in synthetic dimensions

    Hurst, Hilary M.; Wilson, Justin H.; Pixley, J. H.; Spielman, I. B.; Natu, Stefan S.
    The internal degrees of freedom provided by ultracold atoms provide a route for realizing higher dimensional physics in systems with limited spatial dimensions. Nonspatial degrees of freedom in these systems are dubbed “synthetic dimensions.” This connection is useful from an experimental standpoint but complicated by the fact that interactions alter the condensate ground state. Here we use the Gross-Pitaevskii equation to study the ground-state properties of a spin-1 Bose gas under the combined influence of an optical lattice, spatially varying spin-orbit coupling, and interactions at the mean-field level. The associated phases depend on the sign of the spin-dependent interaction parameter...

  14. Quasiparticle explanation of "weak thermalization" regime under quench in a non-integrable quantum spin chain

    Lin, Cheng-Ju; Motrunich, Olexei I.
    Eigenstate Thermalization Hypothesis provides one picture of thermalization in a quantum system by looking at individual eigenstates. However, it is also important to consider how local observables reach equilibrium values dynamically. Quench protocol is one of the settings to study such questions. A recent numerical study [Bañuls, Cirac, and Hastings, Phys. Rev. Lett. 106, 050405 (2011)] of a nonintegrable quantum Ising model with longitudinal field under such quench setting found different behaviors for different initial quantum states. One particular case called "weak thermalization" regime showed apparently persistent oscillations of some observables. Here we provide an explanation of such oscillations. We note...

  15. Jarzynski-like equality for the out-of-time-ordered correlator

    Yunger Halpern, Nicole
    The out-of-time-ordered correlator (OTOC) diagnoses quantum chaos and the scrambling of quantum information via the spread of entanglement. The OTOC encodes forward and reverse evolutions and has deep connections with the flow of time. So do fluctuation relations such as Jarzynski's equality, derived in nonequilibrium statistical mechanics. I unite these two powerful, seemingly disparate tools by deriving a Jarzynski-like equality for the OTOC. The equality's left-hand side equals the OTOC. The right-hand side suggests a protocol for measuring the OTOC indirectly. The protocol is platform-nonspecific and can be performed with weak measurement or with interference. Time evolution need not be...

  16. Dynamical Cooper pairing in nonequilibrium electron-phonon systems

    Knap, Michael; Babadi, Mehrtash; Refael, Gil; Martin, Ivar; Demler, Eugene
    We analyze Cooper pairing instabilities in strongly driven electron-phonon systems. The light-induced nonequilibrium state of phonons results in a simultaneous increase of the superconducting coupling constant and the electron scattering. We demonstrate that the competition between these effects leads to an enhanced superconducting transition temperature in a broad range of parameters. Our results may explain the observed transient enhancement of superconductivity in several classes of materials upon irradiation with high intensity pulses of terahertz light, and may pave new ways for engineering high-temperature light-induced superconducting states.

  17. Quantum information sharing between topologically distinct platforms

    Hou, Chang-Yu; Refael, Gil; Shtengel, Kirill
    Can topological quantum entanglement between anyons in one topological medium “stray” into a different, topologically distinct medium? In other words, can quantum information encoded nonlocally in the combined state of non-Abelian anyons be shared between two distinct topological media? For one-dimensional topological superconductors with Majorana bound states at the end of system, the quantum information store in those Majorana bound states can be transfered by directly coupling nearby Majorana bound states. However, coupling of two one-dimensional Majorana states will produce a gap, indicating that distinct topological regions of one-dimensional wires unite into a single topological region through the information transfer...

  18. Charge metastability and hysteresis in the quantum Hall regime

    Pollanen, J.; Eisenstein, J. P.; Pfeiffer, L. N.; West, K. W.
    We report simultaneous quasi-dc magnetotransport and high-frequency surface acoustic wave measurements on bilayer two-dimensional electron systems in GaAs. Near strong integer quantized Hall states, a strong magnetic-field-sweep hysteresis in the velocity of the acoustic waves is observed at low temperatures. This hysteresis indicates the presence of a metastable state with anomalously high conductivity in the interior of the sample. This nonequilibrium state is not revealed by conventional low-frequency transport measurements which are dominated by dissipationless transport at the edge of the two-dimensional system. We find that a field-cooling technique allows the equilibrium charge configuration within the interior of the sample...

  19. LISA pathfinder appreciably constrains collapse models

    Helou, Bassam; Slagmolen, B. J. J.; McClelland, David E.; Chen, Yanbei
    LISA Pathfinder’s measurement of a relative acceleration noise between two free-falling test masses with a square root of the power spectral density of 5.2±0.1 fm s^(−2)/√Hz [1] appreciably constrains collapse models. In particular, we bound the localization rate parameter, ⋋CSL, in the continuous spontaneous localization model (CSL) to be at most (2.96 ± 0.12) × 10^(−8) s^(−1). Moreover, we bound the regularization scale, σDP, used in the Diosi-Penrose (DP) model to be at least 40.1 ± 0.5 fm. These bounds significantly constrain the validity of these models. In particular: (i) a lower bound of 2.2 × 10^(−8±2)s^(−1) for ⋋CSL has been...

  20. Signatures of Phonon and Defect-Assisted Tunneling in Planar Metal–Hexagonal Boron Nitride–Graphene Junctions

    Chandni, U.; Watanabe, K.; Taniguchi, T.; Eisenstein, J. P.
    Electron tunneling spectroscopy measurements on van der Waals heterostructures consisting of metal and graphene (or graphite) electrodes separated by atomically thin hexagonal boron nitride tunnel barriers are reported. The tunneling conductance, dI/dV, at low voltages is relatively weak, with a strong enhancement reproducibly observed to occur at around |V| ≈ 50 mV. While the weak tunneling at low energies is attributed to the absence of substantial overlap, in momentum space, of the metal and graphene Fermi surfaces, the enhancement at higher energies signals the onset of inelastic processes in which phonons in the heterostructure provide the momentum necessary to link...

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