arXiv subjects

Garry Goldstein

Publications and source records attributed to Garry Goldstein.

41 records · Page 3Linked to original sources

arXiv2014

How to experimentally detect a GGE? - Universal Spectroscopic Signatures of the GGE in the Tonks gas

In this work we study the properties of the density density correlation function of the 1-D Lieb-Liniger model with infinite repulsion in the GGE regime. The GGE describes the equilibrated system in the long time limit after a quench from a generic initial state. In the case that the initial and hence the final state has low entropy per particle we find that the density density correlation function has a universal form, in particular it depends on a few parameters corresponding to "key" momenta and has power law dependence on the distance. This provides an experimental signature of the GGE which may readily be identified through spectroscopy. These signatures are universal and robust to initial sate preparation.

cond-mat.quant-gas↗

arXiv2014

Equilibration and Generalized GGE in the Lieb Liniger gas

We study the nonequilibrium properties of the one dimensional Lieb Liniger model in the finite repulsion regime. Introducing a new version of the Yudson representation applicable to finite size systems and appropriately taking the infinite volume limit we are able to study equilibration of the Lieb Liniger gas in the thermodynamic limit. We provide a formalism to compute various correlation functions for highly non equilibrium initial states. We are able to find explicit analytic expressions for the long time limit of the expectation of the density, density density and related correlation functions. We show that the gas equilibriates to a diagonal ensemble which we show is equivalent to a generalized version of the GGE for sufficiently simple correlation functions, which in particular include density correlations.

cond-mat.quant-gas↗

arXiv2012

Exact Zero Modes in Closed Systems of Interacting Fermions

We show that for closed finite sized systems with an odd number of real fermionic modes, even in the presence of interactions, there are always at least two fermionic operators that commute with the Hamiltonian.There is a zero mode corresponding to the fermion parity operator, as shown by Akhmerov, as well as additional linearly independent zero modes, one of which is 1) the one that is continuously connected to the Majorana mode solution in the non-interacting limit, and 2) less prone to decoherence when the system is opened to contact with an infinite bath. We also show that in the idealized situation where there are two or more well separated zero modes each associated with a finite number of fermions at a localized vortex, these modes have non-Abelian Ising statistics under braiding. Furthermore the algebra of the zero mode operators makes them useful for fermionic quantum computation.

cond-mat.stat-mech↗

arXiv2011

Decay rates for topological memories encoded with Majorana fermions

Recently there have been numerous proposals to create Majorana zero modes in solid state heterojunctions, superconducting wires and optical lattices. Putatively the information stored in qubits constructed from these modes is protected from various forms of decoherence. Here we show that this is not the case. We present a generic method to study the effect of external perturbations on these modes. We focus on the case where there are no interactions between different Majorana modes either directly or through intermediary fermions. To quantify the rate of loss of the information stored in the Majorana modes we study the two-time correlators for qubits built from them. We analyze a generic gapped fermionic environment (bath) interacting via tunneling with different components of the qubit (different Majorana modes). We find that static (time-independent) perturbations are not harmful, and just lead to a depletion of the information stored that saturates in the long-time limit. On the other hand we find markedly different results for dynamic (time dependent) systems, with no coherence surviving in the long time limit. In particular we find that dephasing and energy fluctuations of the modes in the fermionic bath have adverse effects on the Majorana memories.

cond-mat.mes-hall↗

arXiv2010

Quantum Limits on Parameter Estimation

We present a new proof of the quantum Cramer-Rao bound for precision parameter estimation [1-3] and extend it to a more general class of measurement procedures. We analyze a generalized framework for parameter estimation that covers most experimentally accessible situations, where multiple rounds of measurements, auxiliary systems or external control of the evolution are available. The proof presented demonstrates the equivalence of these more general metrology procedures to the simplest optimal strategy for which the bound is proven: a single measurement of a two-level system interacting with a time-independent Hamiltonian.

quant-ph↗