Quantum Information

Quantum mechanics redefines information and its fundamental properties. Researchers at Perimeter Institute work to understand the properties of quantum information and study which information processing tasks are feasible, and which are infeasible or impossible. This includes research in quantum cryptography, which studies the trade-off between information extraction and disturbance, and its applications. It also includes research in quantum error correction, which involves the study of methods for protecting information against decoherence. Another important side of the field is studying the application of quantum information techniques and insights to other areas of physics, including quantum foundations and condensed matter.

Displaying 913 - 924 of 1366

Processing quantum information with relativistic motion of atoms

Eduardo Martin-Martinez University of Waterloo
May 13, 2013

PIRSA:13050017
Quantum Information
Entanglement at strongly-interacting quantum critical points in 2+1D

Roger Melko University of Waterloo
May 10, 2013

PIRSA:13050051
Quantum Information
Twisted Symmetry in Tensor Network States and Topological Order

Oliver Buerschaper Multiverse Computing (Germany)
May 10, 2013

PIRSA:13050048
Quantum Information

Condensed Matter
Spin-orbital quantum liquid on the honeycomb lattice

Philippe Corboz Universiteit van Amsterdam
May 09, 2013

PIRSA:13050045
Quantum Information

Condensed Matter
Characterizing topological spin liquids using PEPS

Norbert Schuch Max Planck Institute for Gravitational Physics - Albert Einstein Institute (AEI)
May 09, 2013

PIRSA:13050044
Quantum Information
Emergence and Entanglement in Matrix Product States

Frank Verstraete Ghent University
May 09, 2013

PIRSA:13050043
Quantum Information
Characterizing topological order form a microscopic lattice Hamiltonian

Lukasz Cincio Los Alamos National Laboratory
May 09, 2013

PIRSA:13050042
Quantum Information

Condensed Matter
Topological Order with a Twist: Ising Anyons from an Abelian Model

Hector Bombin PsiQuantum Corp.
May 06, 2013

PIRSA:13050024
Quantum Information
From Pauli's Principle to Fermionic Entanglement

Matthias Christandl ETH Zurich
May 03, 2013

PIRSA:13050005
Quantum Information

Quantum Foundations
Tensor Networks: an Overview

Lukasz Cincio Los Alamos National Laboratory
April 25, 2013

PIRSA:13040131
Quantum Information
Continuous-variable entanglement distillation and non-commutative central limit theorems

Earl Campbell University of Sheffield
April 15, 2013

PIRSA:13040122
Quantum Information
12/13 PSI - Explorations on Quantum Information Lecture 14

David Cory Institute for Quantum Computing (IQC)
April 05, 2013

PIRSA:13040037
Quantum Information

Processing quantum information with relativistic motion of atoms

Eduardo Martin-Martinez University of Waterloo
May 13, 2013

PIRSA:13050017
Quantum Information
We show that particle detectors, such as 2-level atoms, in non-inertial motion (or in gravitational fields) could be used to build quantum gates for the processing of quantum information. Concretely, we show that through suitably chosen non-inertial trajectories of the detectors the interaction Hamiltonian's time dependence can be modulated to yield arbitrary rotations in the Bloch sphere due to relativistic quantum effects. Ref. Phys. Rev. Lett. 110, 160501 (2013)
Entanglement at strongly-interacting quantum critical points in 2+1D

Roger Melko University of Waterloo
May 10, 2013

PIRSA:13050051
Quantum Information
In two or more spatial dimensions, leading-order contributions to the scaling of entanglement entropy typically follow the "area" or boundary law. Although this leading-order scaling is non-universal, at a quantum critical point (QCP), the sub-leading behavior does contain universal physics. Different universal functions can be access through entangling regions of different geometries. For example, for polygonal shaped regions, quantum field theories have demonstrated that the subleading scaling is logarithmic, with a universal coefficient dependent on the number of vertices in the polygon. Although such universal quantities are routinely studied in non-interacting field theories, it often requires numerical simulation to access them in interacting theories. In this talk, I discuss quantum Monte Carlo (QMC) and numerical Linked-Cluster Expansion (NLCE) calculations of the Renyi entropies at the transverse-field Ising model QCP on the 2D square lattice. We calculate the universal coefficient of the vertex-induced logarithmic scaling term, and compare to non-interacting field theory calculations by Casini and Huerta. Also, we examine the shape dependence of the Renyi entropy for finite-size toroidal lattices with smooth boundaries. Such geometries provide a sensitive probe of the gapless wave function in the thermodynamic limit, and give new universal quantities that could be examined by future field-theoretical studies in 2+1D.
Twisted Symmetry in Tensor Network States and Topological Order

Oliver Buerschaper Multiverse Computing (Germany)
May 10, 2013

PIRSA:13050048
Quantum Information

Condensed Matter
Spin-orbital quantum liquid on the honeycomb lattice

Philippe Corboz Universiteit van Amsterdam
May 09, 2013

PIRSA:13050045
Quantum Information

Condensed Matter
The symmetric Kugel-Khomskii can be seen as a minimal model describing the interactions between spin and orbital degrees of freedom in certain transition-metal oxides with orbital degeneracy, and it is equivalent to the SU(4) Heisenberg model of four-color fermionic atoms. We present simulation results for this model on various two-dimensional lattices obtained with infinite projected-entangled pair states (iPEPS), an efficient variational tensor-network ansatz for two dimensional wave functions in the thermodynamic limit. We find a rich variety of exotic phases: while on the square and checkerboard lattices the ground state exhibits dimer-N\'eel order and plaquette order, respectively, quantum fluctuations on the honeycomb lattice destroy any order, giving rise to a spin-orbital liquid. Our results are supported from flavor-wave theory and exact diagonalization. Furthermore, the properties of the spin-orbital liquid state on the honeycomb lattice are accurately accounted for by a projected variational wave-function based on the pi-flux state of fermions on the honeycomb lattice at 1/4-filling. In that state, correlations are algebraic because of the presence of a Dirac point at the Fermi level, suggesting that the ground state is an algebraic spin-orbital liquid. This model provides a possible starting point to understand the recently discovered spin-orbital liquid behavior of Ba_3CuSb_2O_9. The present results also suggest to choose optical lattices with honeycomb geometry in the search for quantum liquids in ultra-cold four-color fermionic atoms.
Characterizing topological spin liquids using PEPS

Norbert Schuch Max Planck Institute for Gravitational Physics - Albert Einstein Institute (AEI)
May 09, 2013

PIRSA:13050044
Quantum Information
Projected Entangled Pair States (PEPS) provide a local description of correlated many-body states. I will discuss how PEPS can be used to characterize topological spin liquids, in particular Resonating Valence Bond states. On the one hand, I will show how the symmetries in the local PEPS description allow to identify that these states appear as topologically degenerate ground states of local Hamiltonians. On the other hand, I will discuss how from exact diagonalization of the transfer operator one can extract both the topological order and the spin liquid nature of the ground state.
Emergence and Entanglement in Matrix Product States

Frank Verstraete Ghent University
May 09, 2013

PIRSA:13050043
Quantum Information
Characterizing topological order form a microscopic lattice Hamiltonian

Lukasz Cincio Los Alamos National Laboratory
May 09, 2013

PIRSA:13050042
Quantum Information

Condensed Matter
In this talk I will show how to obtain a detailed characterization of the emergent topological order starting from microscopic Hamiltonian on a two dimensional lattice. A key step is to obtain a tensor network representation for a complete set of ground states of the Hamiltonian, ﬁrst on an inﬁnite cylinder and then on a ﬁnite torus. As an application of the method I will study lattice Hamiltonians that give rise to selected anyon models, namely chiral semion, Ising as well as Z_3 and Z_5 models.
Topological Order with a Twist: Ising Anyons from an Abelian Model

Hector Bombin PsiQuantum Corp.
May 06, 2013

PIRSA:13050024
Quantum Information
Anyon models can be symmetric under some permutations of their topological charges. One can then conceive topological defects that, under monodromy, transform anyons according to a symmetry. We study the realization of such defects in the toric code model, showing that a process where defects are braided and fused has the same outcome as if they were Ising anyons.
From Pauli's Principle to Fermionic Entanglement

Matthias Christandl ETH Zurich
May 03, 2013

PIRSA:13050005
Quantum Information

Quantum Foundations
The Pauli exclusion principle is a constraint on the natural occupation numbers of fermionic states. It has been suspected for decades, and only proved very recently, that there is a multitude of further constraints on these numbers, generalizing the Pauli principle. Surprisingly, these constraints are linear: they cut out a geometric object known as a polytope. This is a beautiful mathematical result, but are there systems whose physics is governed by these constraints? In order to address this question, we studied a system of a few fermions connected by springs. As we varied the spring constant, the occupation numbers moved within the polytope. The path they traced hugs very close to the boundary of the polytope, suggesting that the generalized constraints affect the system. I will mention the implications of these findings for the structure of few-fermion ground states and then discuss the relation between the geometry of the polytope and different types of fermionic entanglement.
Tensor Networks: an Overview

Lukasz Cincio Los Alamos National Laboratory
April 25, 2013

PIRSA:13040131
Quantum Information
Tensor network algorithms provide highly competitive tools for analyzing ground state properties of quantum lattice models in one and two spatial dimensions. The most notable examples involve matrix product states, projected entangled pair states and multiscale entanglement renormalization ansatz. The key underlying idea of all the approaches is to decompose a quantum many-body state into a carefully chosen network of tensors.
In this talk I will give an introduction to the subject and show how tensor networks can be used to characterize topological order.
Continuous-variable entanglement distillation and non-commutative central limit theorems

Earl Campbell University of Sheffield
April 15, 2013

PIRSA:13040122
Quantum Information
Entanglement distillation transforms weakly entangled noisy states into highly entangled states, a primitive to be used in quantum repeater schemes and other protocols designed for quantum communication and key distribution. In this work, we present a comprehensive framework for continuous-variable entanglement distillation schemes that convert noisy non-Gaussian states into Gaussian ones in many iterations of the protocol. Instances of these protocols include the recursive Gaussifier protocol and the pumping Gaussifier protocol. The flexibility of these protocols give rise to several beneficial trade-offs related to success probabilities or memory requirements that can be adjusted to reflect experimental specifics. Despite these protocols involving measurements, we relate the convergence in this protocols to new instances of non-commutative central limit theorems. Implications of the findings for quantum repeater schemes are discussed.
12/13 PSI - Explorations on Quantum Information Lecture 14

David Cory Institute for Quantum Computing (IQC)
April 05, 2013

PIRSA:13040037
Quantum Information

Title	Speaker(s)	Date	Talk Type	Info link
Processing quantum information with relativistic motion of atoms	Eduardo Martin-Martinez	2013-05-13	Scientific Series	View details
Entanglement at strongly-interacting quantum critical points in 2+1D	Roger Melko	2013-05-10	Conference	View details
Twisted Symmetry in Tensor Network States and Topological Order	Oliver Buerschaper	2013-05-10	Conference	View details
Spin-orbital quantum liquid on the honeycomb lattice	Philippe Corboz	2013-05-09	Conference	View details
Characterizing topological spin liquids using PEPS	Norbert Schuch	2013-05-09	Conference	View details
Emergence and Entanglement in Matrix Product States	Frank Verstraete	2013-05-09	Conference	View details
Characterizing topological order form a microscopic lattice Hamiltonian	Lukasz Cincio	2013-05-09	Conference	View details
Topological Order with a Twist: Ising Anyons from an Abelian Model	Hector Bombin	2013-05-06	Conference	View details
From Pauli's Principle to Fermionic Entanglement	Matthias Christandl	2013-05-03	Scientific Series	View details
Tensor Networks: an Overview	Lukasz Cincio	2013-04-25	Conference	View details
Continuous-variable entanglement distillation and non-commutative central limit theorems	Earl Campbell	2013-04-15	Scientific Series	View details
12/13 PSI - Explorations on Quantum Information Lecture 14	David Cory	2013-04-05	Course	View details

Quantum Information

Format results