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Eliot Kapit

Publications and source records attributed to Eliot Kapit.

48 records · Page 3Linked to original sources
arXiv2013

Quantum Simulation Architecture for Lattice Bosons in Arbitrary, Tunable External Gauge Fields

We describe a lattice of asymmetrical qubit pairs in one or two dimensions, with couplings arranged so that the motion of single-qubit excited states mimics the behavior of charged lattice bosons hopping in a magnetic field. We show in particular that one can choose the parameters of the many-body circuit to reach a regime where the complex hopping phase between any two elements can be tuned to any value by simply adjusting the relative phases of two applied oscillating voltage signals. We also propose a specific realization of our model using coupled three junction flux qubits, in which one can reach the strongly interacting bosonic quantum Hall limit where one will find anyonic excitations. The circuits could be used for topological quantum computation.

cond-mat.str-el↗
arXiv2011

Non-Abelian Braiding of Lattice Bosons

We report on a numerical experiment in which we use time-dependent potentials to braid non-abelian quasiparticles. We consider lattice bosons in a uniform magnetic field within the fractional quantum Hall regime, where $ν$, the ratio of particles to flux quanta, is near 1/2, 1 or 3/2. We introduce time-dependent potentials which move quasiparticle excitations around one another, explicitly simulating a braiding operation which could implement part of a gate in a quantum computation. We find that different braids do not commute for $ν$ near $1$ and $3/2$, with Berry matrices respectively consistent with Ising and Fibonacci anyons. Near $ν=1/2$, the braids commute.

cond-mat.str-el↗
arXiv2011

Marginal Fermi Liquid from a Partially Nested Fermi Surface and Impurity Scattering in a Two Dimensional Metal

The electron-electron scattering rate of low-energy quasiparticles is computed perturbatively for a two-dimensional metal with a partially nested Fermi surface, a weak electron-electron interaction and an energy-independent impurity scattering rate. We show that even when the nested section comprises only a small fraction of the Fermi surface, the low energy quasiparticle decay rates throughout the Fermi surface gain a term which is linear in energy $ω$. The coefficient of this linear contribution is largest along the nested regions but remains finite elsewhere, and is strongly dependent on the impurity scattering rate $δ$. We discuss the possible relevance of this result to unconventional superconductors (such as the cuprates) and to the normal state of charge density wave materials such as the rare Earth tellurides.

cond-mat.str-el↗
arXiv2011

Even-Odd Correlation Functions on an Optical Lattice

We study how different many body states appear in a quantum gas microscope, such as the one developed at Harvard [Bakr et al. Nature 462, 74 (2009)], where the site-resolved parity of the atom number is imaged. We calculate the spatial correlations of the microscope images, corresponding to the correlation function of the parity of the number of atoms at each site. We produce analytic results for a number of well-known models: noninteracting bosons, the large U Bose-Hubbard model, and noninteracting fermions. We find that these parity correlations tend to be less strong than density-density correlations, but they carry similar information.

cond-mat.quant-gas↗
arXiv2011

Exact Parent Hamiltonian for the Quantum Hall States in a Optical Lattice

We study lattice models of charged particles in uniform magnetic fields. We show how longer range hopping can be engineered to produce a massively degenerate manifold of single-particle ground states with wavefunctions identical to those making up the lowest Landau level of continuum electrons in a magnetic field. We find that in the presence of local interactions, and at the appropriate filling factors, Laughlin's fractional quantum Hall wavefunction is an exact many-body ground state of our lattice model. The hopping matrix elements in our model fall off as a Gaussian, and when the flux per plaquette is small compared to the fundamental flux quantum one only needs to include nearest and next nearest neighbor hoppings. We suggest how to realize this model using atoms in optical lattices, and describe observable consequences of the resulting fractional quantum Hall physics.

cond-mat.quant-gas↗
arXiv2010

Optical Lattice Hamiltonians for Relativistic Quantum Electrodynamics

We show how interpenetrating optical lattices containing Bose-Fermi mixtures can be constructed to emulate the thermodynamics of quantum electrodynamics (QED). We present models of neutral atoms on lattices in 1+1, 2+1 and 3+1 dimensions whose low energy effective action reduces to that of photons coupled to Dirac fermions of the corresponding dimensionality. We give special attention to 2+1 dimensional electrodynamics (QED3) and discuss how two of its most interesting features, chiral symmetry breaking and Chern-Simons physics, could be observed experimentally.

cond-mat.quant-gas↗
arXiv2009

Lorentz Symmetric Quantum Field Theory for Symplectic Fermions

A free quantum field theory with Lorentz symmetry is derived for spin-half symplectic fermions in 2+1 dimensions. In particular, we show that fermionic spin-half fields may be canonically quantized in a free theory with a Klein-Gordon Lagrangian. This theory is shown to have all the required properties of a consistent free quantum field theory, namely causality, unitarity, adherence to the spin-statistics theorem, CPT symmetry, and the Hermiticity and positive definiteness of the Hamiltonian. The global symmetry of the free theory is Sp(4) $\simeq$ SO(5). Possible interacting theories of both the pseudo-Hermitian and Hermitian variety are then examined briefly.

hep-th↗
arXiv2009

Parent Hamiltonian for the Chiral Spin Liquid

We present a method for constructing parent Hamiltonians for the chiral spin liquid. We find two distinct Hamiltonians for which the chiral spin liquid on a square lattice is an exact zero-energy ground state. We diagonalize both Hamiltonians numerically for 16-site lattices, and find that the chiral spin liquid, modulo its two-fold topological degeneracy, is indeed the unique ground state for one Hamiltonian, while it is not unique for the other.

cond-mat.str-el↗
arXiv2009

Non-Fermi liquid properties of 2d symplectic fermions: the role of a dynamically generated (pseudo)-gap

The interacting symplectic fermion model in two spatial dimensions is further analyzed. As an effective low energy theory, the model is unitary. We show that a relativistic mass m is dynamically generated and derive a gap equation for it. By incorporating a finite temperature we study some fundamental properties of the model, such as the specific heat and spin response, which clearly show non-Fermi liquid properties. We find that various physical properties are suppressed at temperatures T< T* where the cross-over scale is T* = m. As a simplified, toy model of high Tc superconductivity, we thus identify the pseudogap energy scale with the zero temperature relativistic mass m, and show that this reproduces some qualitative aspects of the observed phenomenology of the pseudogap. The effects of the pseudogap and finite temperature on the d-wave gap equation are analyzed. In this model, the pseudogap is a distinct phenomenon from superconductivity and in fact competes with it. Our analysis of Tc suggests that the quantum critical point of our model, where the pseudogap vanishes, occurs inside the superconducting dome near optimal doping. For an antiferromagnetic exchange energy of J/k_B ~ 1350K, solutions of the d-wave gap equation give a maximum Tc of about 110K.

cond-mat.str-el↗
arXiv2008

A model of a 2d non-Fermi liquid with SO(5) symmetry, AF order, and a d-wave SC gap

Demanding a consistent quantum field theory description of spin 1/2 particles near a circular Fermi surface in 2d leads to a unique fermionic theory with relevant quartic interactions which has an emergent Lorentz symmetry and automatically has an Sp(4) = SO(5) internal symmetry. The free theory has resistivity linear in temperature. The interacting theory has a low-energy interacting fixed point and is thus a non-Landau/Fermi liquid. Anti-ferromagnetic (AF) and superconducting (SC) order parameters are bilinears in the fields and form the 5-dimensional vector representation of SO(5). An AF phase occurs at low doping which terminates in a first order transition. We incorporate momentum dependent scattering of Cooper pairs near the Fermi surface to 1-loop and derive a new kind of SC gap equation beyond mean field with a d-wave gap solution. Taking into account the renormalization group (RG) scaling properties near the low energy fixed point, we calculate the complete phase diagram as a function of doping, which shows some universal geometric features. The d-wave SC dome terminates on the over-doped side at the fixed point of the RG,which is a quantum critical point. Optimal doping is estimated to occur just below 3/2π^2. The critical temperature for SC at optimal doping is set mainly by the universal nodal Fermi velocity and lattice spacing, and is estimated to average around 140K for LSCO. The pseudogap energy scale is identified as the RG scale of the coupling.

cond-mat.str-el↗
arXiv2008

A unique non-Landau/Fermi liquid in 2d for high Tc superconductivity

It is shown that the main features of the phase diagram for high Tc superconductivity can be calculated as a function of doping in a simple, essentially unique non-Landau/Fermi liquid with quartic interactions. The phase diagram depends on a single parameter 0<gamma<1 determined by the strength of the interaction at short distances. A new d-wave gap equation has solutions that fall under a superconducting dome, which terminates at the renormalization group fixed point. Optimal doping is estimated to occur just below 3/2 π^2. The overall scale for Tc is set by the recently measured universal nodal Fermi velocity and lattice spacing, and is estimated to be 120K < Tc < 160K for LaSrCuO.

cond-mat.str-el↗