Open Access. Powered by Scholars. Published by Universities.®
- Discipline
- Keyword
-
- Quantum physics (40)
- Condensed matter (18)
- Superconductivity (10)
- Classical and quantum mechanics (8)
- General physics (8)
-
- Mesoscale and nanoscale physics (7)
- Quantum field theory (6)
- Physics (4)
- Atomic and molecular physics (3)
- Cosmology (3)
- Physics of elementary particles and fields (3)
- Semiclassical approximation (3)
- Statistical mechanics (3)
- Atomic physics (2)
- Casimir effect (2)
- Computerized simulation (2)
- Control (2)
- Cylinders (2)
- Decoupling (2)
- Engineering (2)
- Field theories (2)
- Fluctuations (2)
- General relativity and quantum cosmology (2)
- General theory of particles & fields (2)
- Instrumentation related to nuclear science and technology (2)
- Markov process (2)
- Other condensed matter (2)
- Performance (2)
- Perturbation theory (2)
- Potentials (2)
Articles 1 - 30 of 68
Full-Text Articles in Quantum Physics
Mermin Inequalities For Perfect Correlations In Many-Qutrit Systems, Jay Lawrence
Mermin Inequalities For Perfect Correlations In Many-Qutrit Systems, Jay Lawrence
Dartmouth Scholarship
The existence of Greenberger-Horne-Zeilinger (GHZ) contradictions in many-qutrit systems was a long-standing theoretical question until its (affirmative) resolution in 2013. To enable experimental tests, we derive Mermin inequalities from concurrent observable sets identified in those proofs. These employ a weighted sum of observables, called M, in which every term has the chosen GHZ state as an eigenstate with eigenvalue unity. The quantum prediction for M is then just the number of concurrent observables, and this grows asymptotically as 2N/3 as the number of qutrits N→∞. The maximum classical value falls short for every N≥3, so that the quantum to classical …
Operator Locality In The Quantum Simulation Of Fermionic Models, Vojtěch Havlíček, Matthias Troyer, James D. Whitfield
Operator Locality In The Quantum Simulation Of Fermionic Models, Vojtěch Havlíček, Matthias Troyer, James D. Whitfield
Dartmouth Scholarship
Simulating fermionic lattice models with qubits requires mapping fermionic degrees of freedom to qubits. The simplest method for this task, the Jordan-Wigner transformation, yields strings of Pauli operators acting on an extensive number of qubits. This overhead can be a hindrance to implementation of qubit-based quantum simulators, especially in the analog context. Here we thus review and analyze alternative fermion-to-qubit mappings, including the two approaches by Bravyi and Kitaev and the Auxiliary Fermion transformation. The Bravyi-Kitaev transform is reformulated in terms of a classical data structure and generalized to achieve a further locality improvement for local fermionic models on a …
Local Spin Operators For Fermion Simulations, James D. Whitfield, Vojtěch Havlíček, Matthias Troyer
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 …
Exact Solution Of Quadratic Fermionic Hamiltonians For Arbitrary Boundary Conditions, Abhijeet Alase, Emilio Cobanera, Gerardo Ortiz, Lorenza Viola
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 …
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
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 …
Superadiabatic Control Of Quantum Operations, Jonathan Vandermause, Chandrasekhar Ramanathan
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 …
Effective Microscopic Models For Sympathetic Cooling Of Atomic Gases, Roberto Onofrio, Bala Sundaram
Effective Microscopic Models For Sympathetic Cooling Of Atomic Gases, Roberto Onofrio, Bala Sundaram
Dartmouth Scholarship
Thermalization of a system in the presence of a heat bath has been the subject of many theoretical investigations especially in the framework of solid-state physics. In this setting, the presence of a large bandwidth for the frequency distribution of the harmonic oscillators schematizing the heat bath is crucial, as emphasized in the Caldeira-Leggett model. By contrast, ultracold gases in atomic traps oscillate at well-defined frequencies and therefore seem to lie outside the Caldeira-Leggett paradigm. We introduce interaction Hamiltonians which allow us to adapt the model to an atomic physics framework. The intrinsic nonlinearity of these models differentiates them from …
Switching Quantum Dynamics For Fast Stabilization, Pierre Scaramuzza, Francesco Ticozzi
Switching Quantum Dynamics For Fast Stabilization, Pierre Scaramuzza, Francesco Ticozzi
Dartmouth Scholarship
Control strategies for dissipative preparation of target quantum states, both pure and mixed, and subspaces are obtained by switching between a set of available semigroup generators. We show that the class of problems of interest can be recast, from a control-theoretic perspective, into a switched-stabilization problem for linear dynamics. This is attained by a suitable affine transformation of the coherence-vector representation. In particular, we propose and compare stabilizing time-based and state-based switching rules for entangled state preparation, showing that the latter not only ensure faster convergence with respect to nonswitching methods, but can be designed so that they retain robustness …
General Transfer-Function Approach To Noise Filtering In Open-Loop Quantum Control, Gerardo A. Paz-Silva, Lorenza Viola
General Transfer-Function Approach To Noise Filtering In Open-Loop Quantum Control, Gerardo A. Paz-Silva, Lorenza Viola
Dartmouth Scholarship
We present a general transfer-function approach to noise filtering in open-loop Hamiltonian engineering protocols for open quantum systems. We show how to identify a computationally tractable set of fundamental filter functions, out of which arbitrary transfer filter functions may be assembled up to arbitrary high order in principle. Besides avoiding the infinite recursive hierarchy of filter functions that arises in general control scenarios, this fundamental filter-functions set suffices to characterize the error suppression capabilities of the control protocol in both the time and frequency domain. We prove that the resulting notion of filtering order reveals conceptually distinct, albeit complementary, …
Robustness Of Composite Pulses To Time-Dependent Control Noise, Chingiz Kabytayev, Todd J. Green, Kaveh Khodjasteh, Michael J. Biercuk, Lorenza Viola, Kenneth R. Brown
Robustness Of Composite Pulses To Time-Dependent Control Noise, Chingiz Kabytayev, Todd J. Green, Kaveh Khodjasteh, Michael J. Biercuk, Lorenza Viola, Kenneth R. Brown
Dartmouth Scholarship
We study the performance of composite pulses in the presence of time-varying control noise on a single qubit. These protocols, originally devised only to correct for static, systematic errors, are shown to be robust to time-dependent non-Markovian noise in the control field up to frequencies as high as ∼10% of the Rabi frequency. Our study combines a generalized filter-function approach with asymptotic dc-limit calculations to give a simple analytic framework for error analysis applied to a number of composite-pulse sequences relevant to nuclear magnetic resonance as well as quantum information experiments. Results include examination of recently introduced concatenated composite pulses …
Fundamental Bounds In Measurements For Estimating Quantum States, Hyang-Tag Lim, Young-Sik Ra, Kang-Hee Hong, Seung-Woo Lee, Yoon-Ho Kim
Fundamental Bounds In Measurements For Estimating Quantum States, Hyang-Tag Lim, Young-Sik Ra, Kang-Hee Hong, Seung-Woo Lee, Yoon-Ho Kim
Dartmouth Scholarship
Quantum measurement unavoidably disturbs the state of a quantum system if any information about the system is extracted. Recently, the concept of reversing quantum measurement has been introduced and has attracted much attention. Numerous efforts have thus been devoted to understanding the fundamental relation of the amount of information obtained by measurement to either state disturbance or reversibility. Here, we experimentally prove the trade-off relations in quantum measurement with respect to both state disturbance and reversibility. By demonstrating the quantitative bound of the trade-off relations, we realize an optimal measurement for estimating quantum systems with minimum disturbance and maximum reversibility. …
Signatures Of The Valley Kondo Effect In Si/Sige Quantum Dots, Mingyun Yuan, R. Joynt, Zhen Yang, Chunyang Tang, D. E. Savage, M. G. Lagally, M. A. Eriksson, A. J. Rimberg
Signatures Of The Valley Kondo Effect In Si/Sige Quantum Dots, Mingyun Yuan, R. Joynt, Zhen Yang, Chunyang Tang, D. E. Savage, M. G. Lagally, M. A. Eriksson, A. J. Rimberg
Dartmouth Scholarship
We report measurements consistent with the valley Kondo effect in Si/SiGe quantum dots, evidenced by peaks in the conductance versus source-drain voltage that show strong temperature dependence. The Kondo peaks show unusual behavior in a magnetic field that we interpret as arising from the valley degree of freedom. The interplay of valley and Zeeman splittings is suggested by the presence of side peaks, revealing a zero-field valley splitting between 0.28 to 0.34 meV. A zero-bias conductance peak for nonzero magnetic field, a phenomenon consistent with valley nonconservation in tunneling, is observed in two samples.
Quantum Resources For Purification And Cooling: Fundamental Limits And Opportunities, Francesco Ticozzi, Lorenza Viola
Quantum Resources For Purification And Cooling: Fundamental Limits And Opportunities, Francesco Ticozzi, Lorenza Viola
Dartmouth Scholarship
Preparing a quantum system in a pure state is ultimately limited by the nature of the system's evolution in the presence of its environment and by the initial state of the environment itself. We show that, when the system and environment are initially uncorrelated and arbitrary joint unitary dynamics is allowed, the system may be purified up to a certain (possibly arbitrarily small) threshold if and only if its environment, either natural or engineered, contains a “virtual subsystem” which has the same dimension and is in a state with the desired purity. Beside providing a unified understanding of quantum purification …
A Cavity-Cooper Pair Transistor Scheme For Investigating Quantum Optomechanics In The Ultra-Strong Coupling Regime, A. J. Rimberg, M. P. Blencowe, A. D. Armour, P. D. Nation
A Cavity-Cooper Pair Transistor Scheme For Investigating Quantum Optomechanics In The Ultra-Strong Coupling Regime, A. J. Rimberg, M. P. Blencowe, A. D. Armour, P. D. Nation
Dartmouth Scholarship
We propose a scheme involving a Cooper pair transistor (CPT) embedded in a superconducting microwave cavity, where the CPT serves as a charge tunable quantum inductor to facilitate ultra-strong coupling between photons in the cavity and a nano- to meso-scale mechanical resonator. The mechanical resonator is capacitively coupled to the CPT, such that mechanical displacements of the resonator cause a shift in the CPT inductance and hence the cavity's resonant frequency. The amplification provided by the CPT is sufficient for the zero point motion of the mechanical resonator alone to cause a significant change in the cavity resonance. Conversely, a …
Exact And Approximate Solutions For The Quantum Minimum-Kullback-Entropy Estimation Problem, Carlo Sparaciari, Stefano Olivares, Francesco Ticozzi, Matteo G. A. Paris
Exact And Approximate Solutions For The Quantum Minimum-Kullback-Entropy Estimation Problem, Carlo Sparaciari, Stefano Olivares, Francesco Ticozzi, Matteo G. A. Paris
Dartmouth Scholarship
The minimum-Kullback-entropy principle (mKE) is a useful tool to estimate quantum states and operations from incomplete data and prior information. In general, the solution of an mKE problem is analytically challenging and an approximate solution has been proposed and employed in different contexts. Recently, the form and a way to compute the exact solution for finite dimensional systems has been found, and a question naturally arises on whether the approximate solution could be an effective substitute for the exact solution, and in which regimes this substitution can be performed. Here, we provide a systematic comparison between the exact and the …
Majorana Flat Bands In S -Wave Gapless Topological Superconductors, Shusa Deng, Gerardo Ortiz, Amrit Poudel, Lorenza Viola
Majorana Flat Bands In S -Wave Gapless Topological Superconductors, Shusa Deng, Gerardo Ortiz, Amrit Poudel, Lorenza Viola
Dartmouth Scholarship
We demonstrate how the nontrivial interplay between spin-orbit coupling and nodeless s-wave superconductivity can drive a fully gapped two-band topological insulator into a time-reversal invariant gapless topological superconductor supporting symmetry-protected Majorana flat bands. We characterize topological phase diagrams by a Z2×Z2 partial Berry-phase invariant, and show that, despite the trivial crystal geometry, no unique bulk-boundary correspondence exists. We trace this behavior to the anisotropic quasiparticle bulk gap closing, linear vs quadratic, and argue that this provides a unifying principle for gapless topological superconductivity. Experimental implications for tunneling conductance measurements are addressed, relevant for lead chalcogenide materials.
Hamiltonian Quantum Simulation With Bounded-Strength Controls, Adam D. Bookatz, Pawel Wocjan, Lorenza Viola
Hamiltonian Quantum Simulation With Bounded-Strength Controls, Adam D. Bookatz, Pawel Wocjan, Lorenza Viola
Dartmouth Scholarship
We propose dynamical control schemes for Hamiltonian simulation in many-body quantum systems that avoid instantaneous control operations and rely solely on realistic bounded-strength control Hamiltonians. Each simulation protocol consists of periodic repetitions of a basic control block, constructed as a modification of an 'Eulerian decoupling cycle,' that would otherwise implement a trivial (zero) target Hamiltonian. For an open quantum system coupled to an uncontrollable environment, our approach may be employed to engineer an effective evolution that simulates a target Hamiltonian on the system while suppressing unwanted decoherence to the leading order, thereby allowing for dynamically corrected simulation. We …
Asymmetric Architecture For Heralded Single-Photon Sources, Luca Mazzarella, Francesco Ticozzi, Alexander V. Sergienko, Giuseppe Vallone, Paolo Villoresi
Asymmetric Architecture For Heralded Single-Photon Sources, Luca Mazzarella, Francesco Ticozzi, Alexander V. Sergienko, Giuseppe Vallone, Paolo Villoresi
Dartmouth Scholarship
Single-photon sources represent a fundamental building block for optical implementations of quantum information tasks ranging from basic tests of quantum physics to quantum communication and high-resolution quantum measurement. In this paper, in order to compare the effectiveness of different designs, we introduce a single-photon source performance index, based on the maximum probability of generating a single photon that still guarantees a given signal-to-noise ratio. We then investigate the performance of a multiplexed system based on asymmetric configuration of multiple heralded single-photon sources. The performance and scalability comparison with both currently existing multiple-source architectures and faint laser configurations reveals an advantage …
Multiband S -Wave Topological Superconductors: Role Of Dimensionality And Magnetic Field Response, Shusa Deng, Gerardo Ortiz, Lorenza Viola
Multiband S -Wave Topological Superconductors: Role Of Dimensionality And Magnetic Field Response, Shusa Deng, Gerardo Ortiz, Lorenza Viola
Dartmouth Scholarship
We further investigate a class of time-reversal-invariant two-band s-wave topological superconductors introduced earlier [Deng, Viola, and Ortiz, Phys. Rev. Lett. 108, 036803 (2012)]. Provided that a sign reversal between the two superconducting pairing gaps is realized, the topological phase diagram can be determined exactly (within mean field) in one and two dimensions as well as in three dimensions upon restricting to the excitation spectrum of time-reversal-invariant momentum modes. We show how, in the presence of time-reversal symmetry, Z2 invariants that distinguish between trivial and nontrivial quantum phases can be constructed by considering only one of the Kramers’ sectors …
Effective Field Theory Approach To Gravitationally Induced Decoherence, M. P. Blencowe
Effective Field Theory Approach To Gravitationally Induced Decoherence, M. P. Blencowe
Dartmouth Scholarship
Adopting the viewpoint that the standard perturbative quantization of general relativity provides an effective description of quantum gravity that is valid at ordinary energies, we show that gravity as an environment induces the rapid decoherence of stationary matter superposition states when the energy differences in the superposition exceed the Planck energy scale.
Automated Synthesis Of Dynamically Corrected Quantum Gates, Kaveh Khodjasteh, Hendrik Bluhm, Lorenza Viola
Automated Synthesis Of Dynamically Corrected Quantum Gates, Kaveh Khodjasteh, Hendrik Bluhm, Lorenza Viola
Dartmouth Scholarship
Dynamically corrected gates are extended to non-Markovian open quantum systems where limitations on the available controls and/or the presence of control noise make existing analytical approaches unfeasible. A computational framework for the synthesis of dynamically corrected gates is formalized that allows sensitivity against non-Markovian decoherence and control errors to be perturbatively minimized via numerical search, resulting in robust gate implementations. Explicit sequences for achieving universal high-fidelity control in a singlet-triplet spin qubit subject to realistic system and control constraint are provided, which simultaneously cancel to the leading order the dephasing due to non-Markovian nuclear-bath dynamics and voltage noise affecting the …
Nanomechanical Resonator Coupled Linearly Via Its Momentum To A Quantum Point Contact, Latchezar L. Benatov, Miles P. Blencowe
Nanomechanical Resonator Coupled Linearly Via Its Momentum To A Quantum Point Contact, Latchezar L. Benatov, Miles P. Blencowe
Dartmouth Scholarship
We use a Born-Markov approximated master equation approach to study the symmetrized-in-frequency current noise spectrum and the oscillator steady state of a nanoelectromechanical system where a nanoscale resonator is coupled linearly via its momentum to a quantum point contact (QPC). Our current noise spectra exhibit clear signatures of the quantum correlations between the QPC current and the back-action force on the oscillator at a value of the relative tunneling phase (η=−π/2) where such correlations are expected to be maximized. We also show that the steady state of the oscillator obeys a classical Fokker-Planck equation, but can experience thermomechanical noise squeezing …
Non-Equilibrium Landauer Transport Model For Hawking Radiation From A Black Hole, P. D. Nation, M. P. Blencowe, Franco Nori
Non-Equilibrium Landauer Transport Model For Hawking Radiation From A Black Hole, P. D. Nation, M. P. Blencowe, Franco Nori
Dartmouth Scholarship
We propose that the Hawking radiation energy and entropy flow rates from a black hole can be viewed as a one-dimensional (1D), non-equilibrium Landauer transport process. Support for this viewpoint comes from previous calculations invoking conformal symmetry in the near-horizon region, which give radiation rates that are identical to those of a single 1D quantum channel connected to a thermal reservoir at the Hawking temperature. The Landauer approach shows in a direct way the particle statistics independence of the energy and entropy fluxes of a black hole radiating into vacuum, as well as one near thermal equilibrium with its environment. …
Majorana Modes In Time-Reversal Invariant S -Wave Topological Superconductors, Shusa Deng, Lorenza Viola, Gerardo Ortiz
Majorana Modes In Time-Reversal Invariant S -Wave Topological Superconductors, Shusa Deng, Lorenza Viola, Gerardo Ortiz
Dartmouth Scholarship
We present a time-reversal invariant s-wave superconductor supporting Majorana edge modes. The multiband character of the model together with spin-orbit coupling are key to realizing such a topological superconductor. We characterize the topological phase diagram by using a partial Chern number sum, and show that the latter is physically related to the parity of the fermion number of the time-reversal invariant modes. By taking the self-consistency constraint on the s-wave pairing gap into account, we also establish the possibility of a direct topological superconductor-to-topological insulator quantum phase transition.
Colloquium : Stimulating Uncertainty: Amplifying The Quantum Vacuum With Superconducting Circuits, P. D. Nation, J. R. Johansson, M. P. Blencowe, Franco Nori
Colloquium : Stimulating Uncertainty: Amplifying The Quantum Vacuum With Superconducting Circuits, P. D. Nation, J. R. Johansson, M. P. Blencowe, Franco Nori
Dartmouth Scholarship
The ability to generate particles from the quantum vacuum is one of the most profound consequences of Heisenberg’s uncertainty principle. Although the significance of vacuum fluctuations can be seen throughout physics, the experimental realization of vacuum amplification effects has until now been limited to a few cases. Superconducting circuit devices, driven by the goal to achieve a viable quantum computer, have been used in the experimental demonstration of the dynamical Casimir effect, and may soon be able to realize the elusive verification of analog Hawking radiation. This Colloquium article describes several mechanisms for generating photons from the quantum vacuum and …
Experimental Characterization Of Coherent Magnetization Transport In A One-Dimensional Spin System, Chandrasekhar Ramanathan, Paola Cappellaro, Lorenza Viola, David G. Cory
Experimental Characterization Of Coherent Magnetization Transport In A One-Dimensional Spin System, Chandrasekhar Ramanathan, Paola Cappellaro, Lorenza Viola, David G. Cory
Dartmouth Scholarship
We experimentally characterize the non-equilibrium, room-temperature magnetization dynamics of a spin chain evolving under an effective double-quantum (DQ) Hamiltonian. We show that the Liouville space operators corresponding to the magnetization and the two-spin correlations evolve 90 degrees out of phase with each other, and drive the transport dynamics. For a nearest-neighbor-coupled N-spin chain, the dynamics are found to be restricted to a Liouville operator space whose dimension scales only as N2, leading to a slow growth of multi-spin correlations. Even though long-range couplings are present in the real system, we find excellent agreement between the analytical predictions …
Pointer States Via Engineered Dissipation, Kaveh Khodjasteh, Viatcheslav V. V. Dobrovitski, Lorenza Viola
Pointer States Via Engineered Dissipation, Kaveh Khodjasteh, Viatcheslav V. V. Dobrovitski, Lorenza Viola
Dartmouth Scholarship
Pointer states are long-lasting high-fidelity states in open quantum systems. We show how any pure state in a non-Markovian open quantum system can be made to behave as a pointer state by suitably engineering the coupling to the environment via open-loop periodic control. Engineered pointer states are constructed as approximate fixed points of the controlled open-system dynamics, in such a way that they are guaranteed to survive over a long time with a fidelity determined by the relative precision with which the dynamics is engineered. We provide quantitative minimum-fidelity bounds by identifying symmetry and ergodicity conditions that the decoherence-inducing perturbation …
Dynamical Critical Scaling And Effective Thermalization In Quantum Quenches: Role Of The Initial State, Shusa Deng, Gerardo Ortiz, Lorenza Viola
Dynamical Critical Scaling And Effective Thermalization In Quantum Quenches: Role Of The Initial State, Shusa Deng, Gerardo Ortiz, Lorenza Viola
Dartmouth Scholarship
We explore the robustness of universal dynamical scaling behavior in a quantum system near criticality with respect to initialization in a large class of states with finite energy. By focusing on a homogeneous XY quantum spin chain in a transverse field, we characterize the nonequilibrium response under adiabatic and sudden quench processes originating from a pure as well as a mixed excited initial state, and involving either a regular quantum critical or a multicritical point. We find that the critical exponents of the ground-state quantum phase transition can be encoded in the dynamical scaling exponents despite the finite energy of …
Coherent-State Transfer Via Highly Mixed Quantum Spin Chains, Paola Cappellaro, Lorenza Viola, Chandrasekhar Ramanathan
Coherent-State Transfer Via Highly Mixed Quantum Spin Chains, Paola Cappellaro, Lorenza Viola, Chandrasekhar Ramanathan
Dartmouth Scholarship
Spin chains have been proposed as quantum wires in many quantum-information processing architectures. Coherent transmission of quantum information in spin chains over short distances is enabled by their internal dynamics, which drives the transport of single-spin excitations in perfectly polarized chains. Given the practical challenge of preparing the chain in a pure state, we propose to use a chain that is initially in the maximally mixed state. We compare the transport properties of pure and mixed-state chains and find similarities that enable the experimental study of pure-state transfer via mixed-state chains. We also demonstrate protocols for the perfect transfer of …
Information-Preserving Structures: A General Framework For Quantum Zero-Error Information, Robin Blume-Kohout, Hui Khoon Ng, David Poulin, Lorenza Viola
Information-Preserving Structures: A General Framework For Quantum Zero-Error Information, Robin Blume-Kohout, Hui Khoon Ng, David Poulin, Lorenza Viola
Dartmouth Scholarship
Quantum systems carry information. Quantum theory supports at least two distinct kinds of information (classical and quantum), and a variety of different ways to encode and preserve information in physical systems. A system’s ability to carry information is constrained and defined by the noise in its dynamics. This paper introduces an operational framework, using information-preserving structures, to classify all the kinds of information that can be perfectly (i.e., with zero error) preserved by quantum dynamics. We prove that every perfectly preserved code has the same structure as a matrix algebra, and that preserved information can always be corrected. We …