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Caltech Authors (170.931 recursos)

Repository of works by Caltech published authors.

Group = IQIM

Mostrando recursos 1 - 20 de 278

  1. Evidence for a quantum-spin-Hall phase in graphene decorated with Bi_2Te_3 nanoparticles

    Hatsuda, K.; Mine, H.; Nakamura, T.; Li, J.; Wu, R.; Alicea, J.; Katsumoto, S.; Haruyama, J.
    Realization of the quantum-spin-Hall effect in graphene devices has remained an outstanding challenge dating back to the inception of the field of topological insulators. Graphene's exceptionally weak spin-orbit coupling-stemming from carbon's low mass-poses the primary obstacle. We experimentally and theoretically study artificially enhanced spin-orbit coupling in graphene via random decoration with dilute Bi2Te3 nanoparticles. Remarkably, multi-terminal resistance measurements suggest the presence of helical edge states characteristic of a quantum-spin-Hall phase; those magnetic-field dependence, X-ray photoelectron spectra, scanning tunneling spectroscopy, and first-principles calculations further support this scenario. These observations highlight a pathway to spintronics and quantum-information applications in graphene-based quantum-spin-Hall platforms.

  2. Steady state of interacting Floquet insulators

    Seetharam, Karthik I.; Bardyn, Charles-Edouard; Lindner, Netanel H.; Rudner, Mark S.; Refael, Gil
    Floquet engineering offers tantalizing opportunities for controlling the dynamics of quantum many body systems and realizing new nonequilibrium phases of matter. However, this approach faces a major challenge: generic interacting Floquet systems absorb energy from the drive, leading to uncontrolled heating which washes away the sought after behavior. How to achieve and control a non-trivial nonequilibrium steady state is therefore of crucial importance. In this work, we study the dynamics of an interacting one-dimensional periodically-driven electronic system coupled to a phonon heat bath. Using the Floquet-Boltzmann equation (FBE) we show that the electronic populations of the Floquet eigenstates can be controlled by the dissipation. We find the regime in which...

  3. Fracton topological order from the Higgs and partial-confinement mechanisms of rank-two gauge theory

    Ma, Han; Hermele, Michael; Chen, Xie
    Fractons are gapped pointlike excitations in d=3 topological ordered phases whose motion is constrained. They have been discovered in several gapped models but a unifying physical mechanism for generating them is still missing. It has been noticed that in symmetric-tensor U(1) gauge theories, charges are fractons and cannot move freely due to, for example, the conservation of not only the charge but also the dipole moment. To connect these theories with fully gapped fracton models, we study Higgs and partial confinement mechanisms in rank-2 symmetric-tensor gauge theories, where charges or magnetic excitations, respectively, are condensed. Specifically, we describe two different...

  4. A Hot Topic in the Quantum Hall Effect

    Alicea, Jason
    Heat transport studies of fractional quantum Hall systems provide evidence for a new phase of matter with potential applications in fault-tolerant quantum computation.

  5. Mott transition and collective charge pinning in electron doped Sr_2IrO_4

    Wang, K.; Bachar, N.; Teyssier, J.; Luo, W.; Rischau, C. W.; Scheerer, G.; de la Torre, A.; Perry, R. S.; Baumberger, F.; van der Marel, D.
    We studied the in-plane dynamic and static charge conductivity of electron doped Sr_2IrO_4 using optical spectroscopy and DC transport measurements. The optical conductivity indicates that the pristine material is an indirect semiconductor with a direct Mott gap of 0.55 eV. Upon substitution of 2% La per formula unit the Mott gap is suppressed except in a small fraction of the material (15%) where the gap survives, and overall the material remains insulating. Instead of a zero energy mode (or Drude peak) we observe a soft collective mode (SCM) with a broad maximum at 40 meV. Doping to 10% increases the...

  6. Characterization of ^(171)Yb^(3+):YVO_4 for photonic quantum technologies

    Kindem, Jonathan M.; Bartholomew, John G.; Woodburn, Philip J. T.; Zhong, Tian; Craiciu, Ioana; Cone, Rufus L.; Thiel, Charles W.; Faraon, Andrei
    Rare-earth ions in crystals are a proven solid-state platform for quantum technologies in the ensemble regime and attractive for new opportunities at the single-ion level. Among the trivalent rare earths, ^(171)Yb^(3+) is unique in that it possesses a single 4f excited-state manifold and is the only paramagnetic isotope with a nuclear spin of 1/2. In this work, we present measurements of the optical and spin properties of ^(171)Yb^(3+):YVO_4 to assess whether this distinct energy-level structure can be harnessed for quantum interfaces. The material was found to possess large optical absorption compared to other rare-earth-doped crystals owing to the combination of...

  7. Quantum Algorithm for Spectral Measurement with a Lower Gate Count

    Poulin, David; Kitaev, Alexei; Steiger, Damian S.; Hastings, Matthew B.; Troyer, Matthias
    We present two techniques that can greatly reduce the number of gates required to realize an energy measurement, with application to ground state preparation in quantum simulations. The first technique realizes that to prepare the ground state of some Hamiltonian, it is not necessary to implement the time-evolution operator: any unitary operator which is a function of the Hamiltonian will do. We propose one such unitary operator which can be implemented exactly, circumventing any Taylor or Trotter approximation errors. The second technique is tailored to lattice models, and is targeted at reducing the use of generic single-qubit rotations, which are...

  8. Efficient code for relativistic quantum summoning

    Wu, Ya-Dong; Khalid, Abdullah; Sanders, Barry C.
    Summoning retrieves quantum information, prepared somewhere in spacetime, at another specified point in spacetime, but this task is limited by the quantum no-cloning principle and the speed-of-light bound. We develop a thorough mathematical framework for summoning quantum information in a relativistic system and formulate a quantum summoning protocol for any valid configuration of causal diamonds in spacetime. For single-qubit summoning, we present a protocol based on a Calderbank–Shor–Steane code that decreases the space complexity for encoding by a factor of two compared to the previous best result and reduces the gate complexity from scaling as the cube to the square...

  9. Controlling rare-earth ions in a nanophotonic resonator using the ac Stark shift

    Bartholomew, John G.; Zhong, Tian; Kindem, Jonathan M.; Lopez-Rios, Raymond; Rochman, Jake; Craiciu, Ioana; Miyazono, Evan; Faraon, Andrei
    On-chip nanophotonic cavities will advance quantum information science and measurement because they enable efficient interaction between photons and long-lived solid-state spins, such as those associated with rare-earth ions in crystals. The enhanced photon-ion interaction creates new opportunities for all-optical control using the ac Stark shift. Toward this end, we characterize the ac Stark interaction between off-resonant optical fields and Nd^(3+)-ion dopants in a photonic crystal resonator fabricated from yttrium orthovanadate (YVO_4). Using photon echo techniques, at a detuning of 160 MHz we measure a maximum ac Stark shift of 2π × 12.3 MHz per intracavity photon, which is large compared...

  10. Faster Methods for Contracting Infinite 2D Tensor Networks

    Fishman, M. T.; Vanderstraeten, L.; Zauner-Stauber, V.; Haegeman, J.; Verstraete, F.
    We revisit the Corner Transfer Matrix Renormalization Group (CTMRG) method of Nishino and Okunishi for contracting 2-dimensional tensor networks, and demonstrate that its performance can be substantially improved by determining the tensors using an eigenvalue solver as opposed to the power method used in CTMRG. We also generalize the variational uniform Matrix Product State (VUMPS) ansatz for diagonalizing 1D quantum Hamiltonians to the case of 2D transfer matrices, and discuss similarities with the corner methods. These two new algorithms will be crucial in improving the performance of variational Projected Entangled Pair State (PEPS) methods.

  11. Commuting-projector Hamiltonians for chiral topological phases built from parafermions

    Son, Jun Ho; Alicea, Jason
    We introduce a family of commuting-projector Hamiltonians whose degrees of freedom involve ℤ_3 parafermion zero modes residing in a parent fractional-quantum-Hall fluid. These commuting-projector models inherit nontrivial Hall conductance from the parent quantum-Hall states in which they are defined, and thus can describe chiral topological phases. The two simplest models in this family emerge from dressing Ising-paramagnet and toric-code spin models with parafermions; we study their edge properties, anyonic excitations, and ground-state degeneracy. We show that the first model realizes a symmetry-enriched topological phase (SET) for which ℤ_2 spin-flip symmetry from the Ising paramagnet permutes the anyons. Interestingly, the interface...

  12. Two dimensional optomechanical crystals for quantum optomechanics

    Pfeifer, Hannes; Ren, Hengjiang; MacCabe, Greg; Painter, Oskar
    Cooling of nanomechanical resonators to their motional ground state [1, 2] triggered recent achievements like non-classical mechanical state preparation [3] or coherent optical to microwave photon conversion [4]. Implementations of such system with optomechanical crystal (OMC) resonators use the co-localization of optical and acoustic modes in a periodically patterned device layer of a silicon-on-insulator (SOI) chip. An initialization of mechanical resonator to low thermal occupations is required by most quantum optomechanical operations. Reaching small thermal mechanical mode occupations and mechanical Q-factors ≳ 10^6 requires pre-cooling to millikelvin temperatures, where even weak optical absorption induces unfavorable local heating [5]. Commonly used...

  13. From Dynamical Localization to Bunching in interacting Floquet Systems

    Baum, Yuval; van Nieuwenburg, Evert P. L.; Refael, Gil
    We show that a quantum many-body system may be controlled by means of Floquet engineering, i.e., their properties may be controlled and manipulated by employing periodic driving. We present a concrete driving scheme that allows control over the nature of mobile units and the amount of diffusion in generic many-body systems. We demonstrate these ideas for the Fermi-Hubbard model, where the drive renders doubly occupied sites (doublons) the mobile excitations in the system. In particular, we show that the amount of diffusion in the system and the level of fermion-pairing may be controlled and understood solely in terms of the doublon dynamics. We find that under certain circumstances...

  14. Locality of Edge States and Entanglement Spectrum from Strong Subadditivity

    Kato, Kohtaro; Brandão, Fernando G. S. L.
    We consider two-dimensional states of matter satisfying an uniform area law for entanglement. We show that the topological entanglement entropy is equal to the minimum relative entropy distance of the edge state of the system to the set of thermal states of local models. The argument is based on strong subadditivity of quantum entropy. For states with zero topological entanglement entropy, in particular, the formula gives locality of the edge states as thermal states of local Hamiltonians. It also implies that the entanglement spectrum of a region is equal to the spectrum of a one-dimensional local thermal state on the boundary of the region. Our result gives a...

  15. Spectral form factors and late time quantum chaos

    Liu, Junyu
    This is a collection of notes that are about spectral form factors of standard ensembles in the random matrix theory, written for the practical usage of current study of late time quantum chaos. More precisely, we consider Gaussian Unitary Ensemble (GUE), Gaussian Orthogonal Ensemble (GOE), Gaussian Symplectic Ensemble (GSE), Wishart-Laguerre Unitary Ensemble (LUE), Wishart-Laguerre Orthogonal Ensemble (LOE), and Wishart-Laguerre Symplectic Ensemble (LSE). These results and their physics applications cover a three-fold classification of late time quantum chaos in terms of spectral form factors.

  16. Enhanced photon-phonon coupling via dimerization in one-dimensional optomechanical crystals

    Matheny, Matthew H.
    We show that dimerization of an optomechanical crystal lattice, which leads to folding of the band diagram, can couple flexural mechanical modes to optical fields within the unit cell via radiation pressure. When compared to currently realized crystals, a substantial improvement in the coupling between photons and phonons is found. For experimental verification, we implement a dimerized lattice in a silicon optomechanical nanobeam cavity and measure a vacuum coupling rate of g_0/2π= 1.7 MHz between an optical resonance at λ_c = 1545 nm and a mechanical resonance at 1.14 GHz.

  17. Reconciling two notions of quantum operator disagreement: Entropic uncertainty relations and information scrambling, united through quasiprobabilities

    Yunger Halpern, Nicole; Bartolotta, Anthony; Pollack, Jason
    How violently do two quantum operators disagree? Different fields of physics feature different measures of incompatibility: (i) In quantum information theory, entropic uncertainty relations constrain measurement outcomes. (ii) In condensed matter and high-energy physics, the out-of-time-ordered correlator (OTOC) signals scrambling, the spread of information through many-body entanglement. We unite these measures, deriving entropic uncertainty relations for scrambling. The entropies are of distributions over weak and strong measurements' possible outcomes. Weakness causes the OTOC quasiprobability (a nonclassical generalization of a probability, in terms of which the OTOC decomposes) to govern terms in the uncertainty bound. Scrambling strengthens the bound, we show, in numerical simulations of a spin chain. Beyond scrambling, we derive...

  18. Resilience of scrambling measurements

    Swingle, Brian; Yunger Halpern, Nicole
    Most experimental protocols for measuring scrambling require time evolution with a Hamiltonian and with the Hamiltonian's negative counterpart (backward time evolution). Engineering controllable quantum many-body systems for which such forward and backward evolution is possible is a significant experimental challenge. Furthermore, if the system of interest is quantum chaotic, one might worry that any small errors in the time reversal will be rapidly amplified, obscuring the physics of scrambling. This paper undermines this expectation: We exhibit a renormalization protocol that extracts nearly ideal out-of-time-ordered-correlator measurements from imperfect experimental measurements. We analytically and numerically demonstrate the protocol's effectiveness, up to the...

  19. Do the surface Fermi arcs in Weyl semimetals survive disorder?

    Wilson, Justin H.; Pixley, J. H.; Huse, David A.; Refael, Gil; Sarma, S. Das
    We theoretically study the topological robustness of the surface physics induced by Weyl Fermi-arc surface states in the presence of short-ranged quenched disorder and surface-bulk hybridization. This is investigated with numerically exact calculations on a lattice model exhibiting Weyl Fermi arcs. We find that the Fermi-arc surface states, in addition to having a finite lifetime from disorder broadening, hybridize with nonperturbative bulk rare states making them no longer bound to the surface (i.e., they lose their purely surface spectral character). Thus, we provide strong numerical evidence that the Weyl Fermi arcs are not topologically protected from disorder. Nonetheless, the surface...

  20. Phase transitions in 3D gravity and fractal dimension

    Dong, Xi; Maguire, Shaun; Maloney, Alexander; Maxfield, Henry
    We show that for three dimensional gravity with higher genus boundary conditions, if the theory possesses a sufficiently light scalar, there is a second order phase transition where the scalar field condenses. This three dimensional version of the holographic superconducting phase transition occurs even though the pure gravity solutions are locally AdS3. This is in addition to the first order Hawking-Page-like phase transitions between different locally AdS3 handlebodies. This implies that the Rényi entropies of holographic CFTs will undergo phase transitions as the Rényi parameter is varied, as long as the theory possesses a scalar operator which is lighter than...

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