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Erich Mueller

Publications and source records attributed to Erich Mueller.

17 recordsLinked to original sources
arXiv2025

Imaging propagating terahertz collective modes in two-dimensional semiconductor double layers

Two-dimensional transition metal dichalcogenide (TMD) semiconductors exhibit a wide range of novel phenomena at millielectronvolt (terahertz-frequency) energy scales, including superconducting and correlation-induced insulating gaps that are frequently accompanied by symmetry breaking. However, due to the subwavelength dimensions and the often low conductivities of these systems, their intrinsic THz plasmons and meV-scale excitation gaps are difficult to access experimentally. Here we report an optical readout method that can image propagating THz-frequency collective modes in real time. The method relies on a strong coupling between the optical polarons of monolayer TMD semiconductors and the local THz fields in a waveguide, which enables us to image THz plasmons with micron scale spatial resolution and determine their propagation group velocities. Moreover, at finite magnetic fields, we observe coherent cyclotron oscillations resulting from Landau level repopulation induced by the THz field. Our findings provide a new near-field platform for probing collective excitations in strongly correlated two-dimensional semiconductors and enable "all-photonic" TMD-based architectures for time-domain THz plasmonics and optoelectronics.

cond-mat.mes-hall↗
arXiv2022

Observation of suppressed viscosity in the normal state of $^3$He due to superfluid fluctuations

By monitoring the quality factor of a quartz tuning fork oscillator we have observed a fluctuation-driven reduction in the viscosity of bulk $^3$He in the normal state near the superfluid transition temperature, $T_c$. These fluctuations, which are only found within $100 \mu$K of $T_c$, play a vital role in the theoretical modeling of ordering; they encode details about the Fermi liquid parameters, pairing symmetry, and scattering phase shifts. They will be of crucial importance for transport probes of the topologically nontrivial features of superfluid $^3$He under strong confinement. Here we characterize the temperature and pressure dependence of the fluctuation signature, finding data collapse consistent with the predicted theoretical behavior.

cond-mat.supr-con↗
arXiv2022

Supercooling of the A phase of $^3$He

Because of the extreme purity, lack of disorder, and complex order parameter, the first-order superfluid $^3$He A-B transition is the leading model system for first order transitions in the early universe. Here we report on the path dependence of the supercooling of the A phase over a wide range of pressures below 29.3 bar at nearly zero magnetic field. The A phase can be cooled significantly below the thermodynamic A-B transition temperature. While the extent of supercooling is highly reproducible, it depends strongly upon the cooling trajectory: The metastability of the A phase is enhanced by transiting through regions where the A phase is more stable. We provide evidence that some of the additional supercooling is due to the elimination of B phase seeds formed upon passage through the superfluid transition. A greater understanding of the physics is essential before the $^3$He can be exploited to model transitions in the early universe.

cond-mat.other↗
arXiv2022

Engineered Dissipation for Quantum Information Science

Quantum information processing relies on precise control of non-classical states in the presence of many uncontrolled environmental degrees of freedom -- requiring careful orchestration of how the relevant degrees of freedom interact with that environment. These interactions are often viewed as detrimental, as they dissipate energy and decohere quantum states. Nonetheless, when controlled, dissipation is an essential tool for manipulating quantum information: Dissipation engineering enables quantum measurement, quantum state preparation, and quantum state stabilization. The progress of quantum device technology, marked by improvements of characteristic coherence times and extensible architectures for quantum control, has coincided with the development of such dissipation engineering tools which interface quantum and classical degrees of freedom. This Review presents dissipation as a fundamental aspect of the measurement and control of quantum devices and highlights the role of dissipation engineering for quantum error correction and quantum simulation that enables quantum information processing on a practical scale.

quant-ph↗
arXiv2021

Path-Dependent Supercooling of the $^3$He Superfluid A-B transition

We examine the discontinuous first-order superfluid $^3$He A to B transition in the vicinity of the polycritical point (2.232 mK and 21.22 bar). We find path-dependent transitions: cooling at fixed pressure yields a well defined transition line in the temperature-pressure plane, but this line can be reliably crossed by depressurizing at nearly constant temperature after transiting $T_{\rm c}$ at a higher pressure. This path dependence is not consistent with any of the standard B-phase nucleation mechanisms in the literature. This symmetry breaking transition is a potential simulator for first order transitions in the early universe.

cond-mat.supr-con↗
arXiv2019

Exact Topological Flat Bands from Continuum Landau Levels

We construct and characterize tight binding Hamiltonians which contain a completely flat topological band made of continuum lowest Landau level wavefunctions sampled on a lattice. We find an infinite family of such Hamiltonians, with simple analytic descriptions. These provide a valuable tool for constructing exactly solvable models. We also implement a numerical algorithm for finding the most local Hamiltonian with a flat Landau level. We find intriguing structures in the spatial dependence of the matrix elements for this optimized model. The models we construct serve as foundations for numerical and experimental studies of topological systems, both non-interacting and interacting.

cond-mat.str-el↗
arXiv2016

Disappearance of Quasiparticles in a Bose Lattice Gas

We use a momentum-space hole-burning technique implemented via stimulated Raman transitions to measure the momentum relaxation time for a gas of bosonic atoms trapped in an optical lattice. By changing the lattice potential depth, we observe a smooth crossover between relaxation times larger and smaller than the bandwidth. The latter condition violates the Mott-Ioffe-Regal bound and indicates a breakdown of the quasi-particle picture. We produce a simple kinetic model that quantitatively predicts these relaxation times. Finally, we introduce a cooling technique based upon our hole-burning technique.

cond-mat.quant-gas↗
arXiv2016

Dynamics of pattern-loaded fermions in bichromatic optical lattices

Motivated by experiments in Munich (M. Schreiber et. al. Science \textbf{349}, 842), we study the dynamics of interacting fermions initially prepared in charge density wave states in one-dimensional bichromatic optical lattices. The experiment sees a marked lack of thermalization, which has been taken as evidence for an interacting generalization of Anderson localization, dubbed "many-body localization". We model the experiments using an interacting Aubry-Andre model and develop a computationally efficient low-density cluster expansion to calculate the even-odd density imbalance as a function of interaction strength and potential strength. Our calculations agree with the experimental results and shed light on the phenomena. We also explore a two-dimensional generalization. The cluster expansion method we develop should have broad applicability to similar problems in non-equilibrium quantum physics.

cond-mat.quant-gas↗
arXiv2014

Floquet Edge States with Ultracold Atoms

We describe an experimental setup for imaging topologically protected Floquet edge states using ultracold bosons in an optical lattice. Our setup involves a deep two dimensional optical lattice with a time dependent superlattice that modulates the hopping between neighboring sites. The finite waist of the superlattice beam yields regions with different topological numbers. One can observe chiral edge states by imaging the real-space density of a bosonic packet launched from the boundary between two topologically distinct regions.

cond-mat.quant-gas↗
arXiv2013

Anytime computation algorithms for approach-evasion differential games

This paper studies a class of approach-evasion differential games, in which one player aims to steer the state of a dynamic system to the given target set in minimum time, while avoiding some set of disallowed states, and the other player desires to achieve the opposite. We propose a class of novel anytime computation algorithms, analyze their convergence properties and verify their performance via a number of numerical simulations. Our algorithms significantly outperform the multi-grid method for the approach-evasion differential games both theoretically and numerically. Our technical approach leverages incremental sampling in robotic motion planning and viability theory.

math.OC↗
arXiv2013

Magnetic polarons in two-component hard core bosons

We use a high-temperature expansion to explore spin correlations around a single hole in a two- dimensional lattice filled with a hard-core two component bose gas. We find that the spins around the hole develop ferromagnetic order and quantify the degree of polarization at temperatures of order the hopping energy, finding a measurably nonzero polarization. We also discuss the effect of fixing the overall magnetization of the system for finite-sized systems.

cond-mat.quant-gas↗
arXiv2011

Vortex structures of a two-component BEC for large anisotropies

We calculate the vortex structures of an elongated two-component Bose-Einstein condensate. We study how these structures depend on the intra-component and inter-component interaction strengths. We present analytic and numeric results respectively at weak and strong interactions; finding lattices with different interlocking geometries: triangular, square, rectangular and double-core.

cond-mat.quant-gas↗
arXiv2011

Study of Supersolidity and Shear Modulus Anomaly of 4He in a Triple Compound Oscillator

The recently discovered shear modulus anomaly in solid 4He bears a strong similarity to the phenomenon of supersolidity in solid 4He and can lead to the period shift and dissipative signals in torsional oscillator experiments that are nearly identical to the classic NCRI signals observed by Kim and Chan. In the experiments described here, we attempt to isolate the effects of these two phenomena on the resonance periods of torsion oscillators. We have constructed a triple compound oscillator with distinct normal modes. We are able to demonstrate that, for this oscillator, the period shifts observed below 200 mK have their primary origin in the temperature dependence of the shear modulus of the solid 4He sample rather than the formation of a supersolid state.

cond-mat.other↗
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

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↗