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Series

Dartmouth College

2016

Articles 1 - 9 of 9

Full-Text Articles in Physics

All-Optical Cooling Of Fermi Gases Via Pauli Inhibition Of Spontaneous Emission, Roberto Onofrio Nov 2016

All-Optical Cooling Of Fermi Gases Via Pauli Inhibition Of Spontaneous Emission, Roberto Onofrio

Dartmouth Scholarship

A technique is proposed to cool Fermi gases to the regime of quantum degeneracy based on the expected inhibition of spontaneous emission due to the Pauli principle. The reduction of the linewidth for spontaneous emission originates a corresponding reduction of the Doppler temperature, which under specific conditions may give rise to a runaway process through which fermions are progressively cooled. The approach requires a combination of a magneto-optical trap as a cooling system and an optical dipole trap to enhance quantum degeneracy. This results in expected Fermi degeneracy factors T/TF comparable to the lowest values recently achieved, with potential for …

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Pattern Phase Transitions Of Self-Propelled Particles: Gases, Crystals, Liquids, And Mills, Zhao Cheng, Zhiyong Chen, Tamás Vicsek, Duxin Chen Oct 2016

Pattern Phase Transitions Of Self-Propelled Particles: Gases, Crystals, Liquids, And Mills, Zhao Cheng, Zhiyong Chen, Tamás Vicsek, Duxin Chen

Dartmouth Scholarship

To understand the collective behaviors of biological swarms, flocks, and colonies, we investigated the non-equilibrium dynamic patterns of self-propelled particle systems using statistical mechanics methods and H-stability analysis of Hamiltonian systems. By varying the individual vision range, we observed phase transitions between four phases, i.e., gas, crystal, liquid, and mill-liquid coexistence patterns. In addition, by varying the inter-particle force, we detected three distinct milling sub-phases, i.e., ring, annulus, and disk. Based on the coherent analysis for collective motions, one may predict the stability and adjust the morphology of the phases of self-propelled particles, which has promising potential applications in …

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Local Spin Operators For Fermion Simulations, James D. Whitfield, Vojtěch Havlíček, Matthias Troyer Sep 2016

Local Spin Operators For Fermion Simulations, James D. Whitfield, Vojtěch Havlíček, Matthias Troyer

Dartmouth Scholarship

Digital quantum simulation of fermionic systems is important in the context of chemistry and physics. Simulating fermionic models on general purpose quantum computers requires imposing a fermionic algebra on qubits. The previously studied Jordan-Wigner and Bravyi-Kitaev transformations are two techniques for accomplishing this task. Here, we reexamine an auxiliary fermion construction which maps fermionic operators to local operators on qubits. The local simulation is performed by relaxing the requirement that the number of qubits should match the number of single-particle states. Instead, auxiliary sites are introduced to enable nonconsecutive fermionic couplings to be simulated with constant low-rank tensor products on …

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Discrimination Between Spin-Dependent Charge Transport And Spin-Dependent Recombination In Π-Conjugated Polymers By Correlated Current And Electroluminescence-Detected Magnetic Resonance, Marzieh Kavand, Douglas Baird, Kipp Van Schooten, Hans Malissa Aug 2016

Discrimination Between Spin-Dependent Charge Transport And Spin-Dependent Recombination In Π-Conjugated Polymers By Correlated Current And Electroluminescence-Detected Magnetic Resonance, Marzieh Kavand, Douglas Baird, Kipp Van Schooten, Hans Malissa

Dartmouth Scholarship

Spin-dependent processes play a crucial role in organic electronic devices. Spin coherence can give rise to spin mixing due to a number of processes such as hyperfine coupling, and leads to a range of magnetic field effects. However, it is not straightforward to differentiate between pure single-carrier spin-dependent transport processes which control the current and therefore the electroluminescence, and spin-dependent electron-hole recombination which determines the electroluminescence yield and in turn modulates the current. We therefore investigate the correlation between the dynamics of spin-dependent electric current and spin-dependent electroluminescence in two derivatives of the conjugated polymer poly(phenylene-vinylene) using simultaneously measured pulsed …

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Exact Solution Of Quadratic Fermionic Hamiltonians For Arbitrary Boundary Conditions, Abhijeet Alase, Emilio Cobanera, Gerardo Ortiz, Lorenza Viola Aug 2016

Exact Solution Of Quadratic Fermionic Hamiltonians For Arbitrary Boundary Conditions, Abhijeet Alase, Emilio Cobanera, Gerardo Ortiz, Lorenza Viola

Dartmouth Scholarship

We present a procedure for exactly diagonalizing finite-range quadratic fermionic Hamiltonians with arbitrary boundary conditions in one of D dimensions, and periodic in the remaining D−1. The key is a Hamiltonian-dependent separation of the bulk from the boundary. By combining information from the two, we identify a matrix function that fully characterizes the solutions, and may be used to construct an efficiently computable indicator of bulk-boundary correspondence. As an illustration, we show how our approach correctly describes the zero-energy Majorana modes of a time-reversal-invariant s-wave two-band superconductor in a Josephson ring configuration, and predicts that a fractional 4π-periodic Josephson effect …

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Inflation And The Quantum Measurement Problem, Stephon Alexander, Dhrubo Jyoti, João Magueijo Aug 2016

Inflation And The Quantum Measurement Problem, Stephon Alexander, Dhrubo Jyoti, João Magueijo

Dartmouth Scholarship

We propose a solution to the quantum measurement problem in inflation. Our model treats Fourier modes of cosmological perturbations as analogous to particles in a weakly interacting Bose gas. We generalize the idea of a macroscopic wave function to cosmological fields, and construct a self-interaction Hamiltonian that focuses that wave function. By appropriately setting the coupling between modes, we obtain the standard adiabatic, scale-invariant power spectrum. Because of central limit theorem, we recover a Gaussian random field, consistent with observations.

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A Proposal On Culling & Filtering A Coxeter Group For 4d, N = 1 Spacetime Susy Representations: Revised, D. E. A. Gates, S. James Gates, Kory Stiffler Aug 2016

A Proposal On Culling & Filtering A Coxeter Group For 4d, N = 1 Spacetime Susy Representations: Revised, D. E. A. Gates, S. James Gates, Kory Stiffler

Dartmouth Scholarship

We present an expanded and detailed discussion of the mathematical tools required to cull and filter representations of the Coxeter Group BC 4 into providing bases for the construction of minimal off-shell representations of the 4D, N" role="presentation" style="box-sizing: border-box; display: inline-table; line-height: normal; letter-spacing: normal; word-spacing: normal; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px; margin: 0px; position: relative;">NN = 1 spacetime supersymmetry algebra.

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Dynamical Decoupling Sequences For Multi-Qubit Dephasing Suppression And Long-Time Quantum Memory, Gerardo A. Paz-Silva, Seung-Woo Lee, Todd J. Green, Lorenza Viola Jul 2016

Dynamical Decoupling Sequences For Multi-Qubit Dephasing Suppression And Long-Time Quantum Memory, Gerardo A. Paz-Silva, Seung-Woo Lee, Todd J. Green, Lorenza Viola

Dartmouth Scholarship

We consider a class of multi-qubit dephasing models that combine classical noise sources and linear coupling to a bosonic environment, and are controlled by arbitrary sequences of dynamical decoupling pulses. Building on a general transfer filter-function framework for open-loop control, we provide an exact representation of the controlled dynamics for arbitrary stationary non-Gaussian classical and quantum noise statistics, with analytical expressions emerging when all dephasing sources are Gaussian. This exact characterization is used to establish two main results. First, we construct multi-qubit sequences that ensure maximum high-order error suppression in both the time and frequency domain and that can be …

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Superadiabatic Control Of Quantum Operations, Jonathan Vandermause, Chandrasekhar Ramanathan May 2016

Superadiabatic Control Of Quantum Operations, Jonathan Vandermause, Chandrasekhar Ramanathan

Dartmouth Scholarship

Adiabatic pulses are used extensively to enable robust control of quantum operations. We introduce an approach to adiabatic control that uses the superadiabatic quality factor as a performance metric to design robust, high-fidelity pulses. This approach permits the systematic design of quantum control schemes to maximize the adiabaticity of a unitary operation in a particular time interval given the available control resources. The interplay between adiabaticity, fidelity, and robustness of the resulting pulses is examined for the case of single-qubit inversion, and superadiabatic pulses are demonstrated to have improved robustness to control errors. A numerical search strategy is developed to …

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