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 877 - 888 of 1290

Information Theoretic Benefit of Entanglement in Classical Communication Settings

Salman Beigi Institute for Research in Fundamental Sciences (IPM)
May 27, 2013

PIRSA:13050077
Quantum Physics
On the non-extendibility of quantum theory
May 27, 2013

PIRSA:13050059
Quantum Physics
Processing quantum information with relativistic motion of atoms

Eduardo Martin-Martinez University of Waterloo
May 13, 2013

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

Roger Melko University of Waterloo
May 10, 2013

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

Oliver Buerschaper Multiverse Computing (Germany)
May 10, 2013

PIRSA:13050048
Quantum Physics

Condensed Matter
Spin-orbital quantum liquid on the honeycomb lattice

Philippe Corboz Universiteit van Amsterdam
May 09, 2013

PIRSA:13050045
Quantum Physics

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 Physics
Emergence and Entanglement in Matrix Product States

Frank Verstraete Ghent University
May 09, 2013

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

Lukasz Cincio Los Alamos National Laboratory
May 09, 2013

PIRSA:13050042
Quantum Physics

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

Hector Bombin PsiQuantum Corp.
May 06, 2013

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

Matthias Christandl ETH Zurich
May 03, 2013

PIRSA:13050005
Quantum Physics

Quantum Physics
Tensor Networks: an Overview

Lukasz Cincio Los Alamos National Laboratory
April 25, 2013

PIRSA:13040131
Quantum Physics

Information Theoretic Benefit of Entanglement in Classical Communication Settings

Salman Beigi Institute for Research in Fundamental Sciences (IPM)
May 27, 2013

PIRSA:13050077
Quantum Physics
Expressions of several information theoretic quantities involve an optimization over auxiliary quantum registers. Entanglement-assisted version of some classical communication problems provides examples of such expressions. Evaluating these expressions requires bounds on the dimension of these auxiliary registers. In the classical case such a bound can usually be obtained based on the
Caratheodory theorem, but we know almost no method to bound the dimension of auxiliary quantum registers. In this talk to compare the classical and quantum sides of the problem the notion of “quantum convexification” will be defined. It will be shown that quantum convexification is strictly richer that the usual classical convexification. Moreover some techniques will be discussed which might be useful for bounding the dimension of quantum auxiliary registers.
On the non-extendibility of quantum theory
May 27, 2013

PIRSA:13050059
Quantum Physics
I will present a recent theorem that asserts that there cannot exist an "extension of quantum theory" that allows us to make more informative predictions about future measurable events (e.g., whether a horizontally polarized photon passes a polarization filter with a given orientation) than standard quantum theory. The theorem is based on two assumptions about the extended theory: (i) the theory should be compatible with quantum theory (this means, in practice, that the theory is not falsified by current experimental data); (ii) the theory should not preclude experimenters from freely choosing the measurement settings. More precisely, the latter assumption corresponds to the requirement that measurement settings can be chosen at random such that they are independent of any other events, except of course those that lie in the causal future of the choice (i.e., in its future light cone). In addition, I will discuss a corollary of the non-extendibility theorem which leads to the same conclusions as a recent theorem by Pusey, Barrett, and Rudolph on the "reality of the quantum state", based only on the above assumptions.
Processing quantum information with relativistic motion of atoms

Eduardo Martin-Martinez University of Waterloo
May 13, 2013

PIRSA:13050017
Quantum Physics
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 Physics
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 Physics

Condensed Matter
Spin-orbital quantum liquid on the honeycomb lattice

Philippe Corboz Universiteit van Amsterdam
May 09, 2013

PIRSA:13050045
Quantum Physics

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 Physics
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 Physics
Characterizing topological order form a microscopic lattice Hamiltonian

Lukasz Cincio Los Alamos National Laboratory
May 09, 2013

PIRSA:13050042
Quantum Physics

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 Physics
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 Physics

Quantum Physics
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 Physics
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.

Title	Speaker(s)	Date	Talk Type	Info link
Information Theoretic Benefit of Entanglement in Classical Communication Settings	Salman Beigi	2013-05-27	Scientific Series	View details
On the non-extendibility of quantum theory		2013-05-27	Conference	View details
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

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Quantum Information

Format results

Information Theoretic Benefit of Entanglement in Classical Communication Settings

On the non-extendibility of quantum theory

Processing quantum information with relativistic motion of atoms

Entanglement at strongly-interacting quantum critical points in 2+1D

Twisted Symmetry in Tensor Network States and Topological Order

Spin-orbital quantum liquid on the honeycomb lattice

Characterizing topological spin liquids using PEPS

Emergence and Entanglement in Matrix Product States

Characterizing topological order form a microscopic lattice Hamiltonian

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

From Pauli's Principle to Fermionic Entanglement

Tensor Networks: an Overview