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 1069 - 1080 of 1359

A Computational Grand-Unified Theory
February 03, 2010

PIRSA:10020037
Quantum Information

Quantum Foundations
Quantum Money

Scott Aaronson The University of Texas at Austin
January 27, 2010

PIRSA:10010078
Quantum Information
The Computational Complexity of Linear Optics

Scott Aaronson The University of Texas at Austin
January 25, 2010

PIRSA:10010009
Quantum Information
Random quantum satisfiability: statistical mechanics of quantum optimization

Chris Laumann Boston University
December 14, 2009

PIRSA:09120031
Quantum Information
Concentration of measure and the mean energy ensemble

Markus Müller Institute for Quantum Optics and Quantum Information (IQOQI) - Vienna
December 07, 2009

PIRSA:09120030
Quantum Information
Unified approach to classical and quantum dualities

Gerardo Ortiz Indiana University - Bloomington
November 18, 2009

PIRSA:09110001
Quantum Information
Why Does Nature Like the Square Root of Negative One?

William Wootters Williams College
November 18, 2009

PIRSA:09110036
Quantum Information
Quantum computational phases of matter: measurement-based quantum computing in the Haldane phase

Stephen Bartlett University of Sydney
November 04, 2009

PIRSA:09110025
Quantum Information
Lecture Series presented by KPMG - Quantum Foundations: From Plato's Cave to Bertlmann's Socks

Robert Spekkens Perimeter Institute for Theoretical Physics
October 25, 2009

PIRSA:09100013
Quantum Information
Harnessing Quantum Physics
- Michele Mosca Institute for Quantum Computing (IQC)
- Daniel Gottesman University of Maryland, College Park
- Dorit Aharonov Hebrew University of Jerusalem
- Ignacio Cirac Max Planck Institute for Gravitational Physics - Albert Einstein Institute (AEI)
- Peter Shor Massachusetts Institute of Technology (MIT) - Department of Mathematics
- Avi Wigderson Institute for Advanced Study (IAS)
October 18, 2009

PIRSA:09100032
Quantum Information
Lecture Series presented by KPMG - Everyday Uses for Quantum Processors

David Cory Institute for Quantum Computing (IQC)
October 17, 2009

PIRSA:09100005
Quantum Information
Adiabatic quantum optimization fails for random instances of NP-complete problems

Jeremie Roland NEC Laboratories America (Princeton)
October 07, 2009

PIRSA:09100099
Quantum Information

A Computational Grand-Unified Theory
February 03, 2010

PIRSA:10020037
Quantum Information

Quantum Foundations
Are Quantum Mechanics and Special Relativity unrelated theories? Is Quantum Field Theory an additional theoretical layer over them? Where the quantization rules and the Plank constant come from? All these questions can find answer in the computational paradigm: "the universe is a huge quantum computer". In my talk I'll take the computational-universe paradigm as genuine theoretical framework, and analyze some relevant implications. A new kind of quantum field theory emerges: "Quantum-Computational Field Theory" (QCFT). I will show how in QCFT Special Relativity unfolds from the fabric of the computational network, which also naturally embeds gauge-invariance, and even the quantization rule and the Planck constant, which thus resort to being properties of the underlying causal tapestry of space-time. In this way Quantum Mechanics remains the only theory needed to describe the computational-universe. I will analyze few simple toy-models in order to explore the mathematical structure of QCFT. The new QCFT has many advantages versus the customary field theoretical framework, solving a number of logical and mathematical problems that plague quantum field theory. One further advantage of QCFT is the possibility of changing the computational engine without changing the field-theoretical framework. One can thus consider different kind of engines, e.g. classical, quantum, super-quantum, and even input-output networks with no pre-established causal relations, which are very interesting for addressing the problem of Quantum Gravity. QCFT opens a large research line: I argue that this program should be addressed soon in the particle physics domain, before entering Quantum Gravity, notwithstanding the experimental success of the usual quantum field theory. It will also be the first test of the Lucien Hardy's program on Quantum Gravity. Reference: arXiv:1001.1088 (http://arxiv.org/abs/1001.1088)
Quantum Money

Scott Aaronson The University of Texas at Austin
January 27, 2010

PIRSA:10010078
Quantum Information
Ever since there's been money, there have been people trying to counterfeit it, and governments trying to stop them. In 1969, the physicist Stephen Wiesner raised the remarkable possibility of money whose authenticity would be guaranteed by the laws of quantum mechanics. However, the question of whether one can have secure quantum money that anyone (not only the bank) can verify has remained open for forty years. In this talk, I'll tell you about progress on the question over the last two years. (1) I'll show that no publicly-verifiable quantum money scheme can have security based on quantum physics alone: like in most cryptography, one also needs a computational hardness assumption. (2) I'll show that one can have quantum money that remains hard to counterfeit, even if a counterfeiter gains access to a "black box" for verifying the money. (3) I'll describe a candidate quantum money scheme I proposed last spring, and how that scheme was recently broken by Lutomirski et al. I'll also discuss a new class of schemes that might evade the existing attacks -- schemes with the bizarre property that not even the bank can prepare the same bill twice. The talk is designed to be accessible to those without a quantum information background. Reference for (1)-(2): S. Aaronson, "Quantum copy-protection and quantum money," in Proceedings of CCC'2009, http://www.scottaaronson.com/papers/noclone-ccc.pdf. Reference for (3): A. Lutomirski, S. Aaronson, E. Farhi, D. Gosset, A. Hassidim, J. Kelner, and P. Shor. Breaking and making quantum money: toward a new quantum cryptographic protocol, Proceedings of Innovations in Computer Science (ICS), 2010. http://arxiv.org/abs/0912.3825.
The Computational Complexity of Linear Optics

Scott Aaronson The University of Texas at Austin
January 25, 2010

PIRSA:10010009
Quantum Information
I'll discuss some work-in-progress about the computational complexity of simulating the extremely "simple" quantum systems that arise in linear optics experiments. I'll show that *either* one can describe an experiment, vastly easier than building a universal quantum computer, that would test whether Nature is performing nontrivial quantum computation, or else one can give surprising new algorithms for approximating the permanent. Audience feedback as to which of these possibilities is the right one is sought. Joint work with Alex Arkhipov.
Random quantum satisfiability: statistical mechanics of quantum optimization

Chris Laumann Boston University
December 14, 2009

PIRSA:09120031
Quantum Information
Alongside the effort underway to build quantum computers, it is important to better understand which classes of problems they will find easy and which others even they will find intractable. Inspired by the success of the statistical study of classical constraint optimization problems, we study random ensembles of the QMA$_1$-complete quantum satisfiability (QSAT) problem introduced by Bravyi. QSAT appropriately generalizes the NP-complete classical satisfiability (SAT) problem. We show that, as the density of clauses/projectors is varied, the ensembles exhibit quantum phase transitions between phases that are product satisfiable, entangled satisfiable and unsatisfiable. Remarkably, almost all instances of QSAT for a fixed interaction graph exhibit the same dimension of the satisfying manifold. This establishes the generic QSAT decision problem as equivalent to a purely graph theoretic property and that the hardest typical instances are likely to be localized in a bounded range of clause density. Based on papers: C.R. Laumann, R. Moessner, A. Scardicchio, and S.L. Sondhi. Phase transitions and random quantum satisfiability. QIC 10 (1/2), (2009). arXiv:0903.1904 C.R. Laumann, A.M. Lauchli, R. Moessner, A. Scardicchio, and S.L. Sondhi. On product, generic and random generic quantum satisfiability. arXiv:0910.2058
Concentration of measure and the mean energy ensemble

Markus Müller Institute for Quantum Optics and Quantum Information (IQOQI) - Vienna
December 07, 2009

PIRSA:09120030
Quantum Information
If a pure quantum state is drawn at random, this state will almost surely be almost maximally entangled. This is a well-known example for the "concentration of measure" phenomenon, which has proved to be tremendously helpful in recent years in quantum information theory. It was also used as a new method to justify some foundational aspects of statistical mechanics. In this talk, I discuss recent work with David Gross and Jens Eisert on concentration in the set of pure quantum states with fixed mean energy: We show typicality in this manifold of quantum states, and give a method to evaluate expectation values explicitly. This involves some interesting mathematics beyond Levy's Lemma, and suggests potential applications such as finding stronger counterexamples to the additivity conjecture.
Unified approach to classical and quantum dualities

Gerardo Ortiz Indiana University - Bloomington
November 18, 2009

PIRSA:09110001
Quantum Information
Dualities appear in nearly all disciplines of physics and play a central role in statistical mechanics and field theory. I will discuss in a pedagogical way our recent findings motivated by a quest for a simple unifying framework for the detection and treatment of dualities. I will explain how classical and quantum dualities, as well as duality relations that appear only in a sector of certain theories (i.e. emergent dualities), can be unveiled, and systematically established. Our method relies on the use of morphisms of the "bond algebra" of a quantum Hamiltonian. Dualities are characterized as unitary mappings implementing such morphisms, whose even powers become symmetries of the quantum problem. Dual variables (non-local mappings between the elementary degrees of freedom of the theory) which were guessed in the past can be derived in our formalism. New self-dualities for four-dimensional Abelian gauge field theories will be discussed.
Why Does Nature Like the Square Root of Negative One?

William Wootters Williams College
November 18, 2009

PIRSA:09110036
Quantum Information
Is there a theory yet to be discovered that underlies quantum theory and explains its structure? If there is such a theory, one of the features it will have to explain is the central role of complex numbers as probability amplitudes. In this talk I explore the physical meaning of the statement “probability amplitudes are complex” by comparing ordinary complex-vector- space quantum theory with the real-vector-space theory having the same basic structure. Specifically, I discuss three questions that bring out qualitative differences between the two theories: (i) Is information about a preparation expressed optimally in the outcomes of a measurement? (ii) Are multipartite states locally accessible? (iii) Is entanglement “monogamous”?
Quantum computational phases of matter: measurement-based quantum computing in the Haldane phase

Stephen Bartlett University of Sydney
November 04, 2009

PIRSA:09110025
Quantum Information
A recent breakthrough in quantum computing has been the realization that quantum computation can proceed solely through single-qubit measurements on an appropriate quantum state. One exciting prospect is that the ground or low-temperature thermal state of an interacting quantum many-body system can serve as such a resource state for quantum computation. The system would simply need to be cooled sufficiently and then subjected to local measurements. It would be unfortunate, however, if the usefulness of a ground or low-temperature thermal state for quantum computation was critically dependent on the details of the system's Hamiltonian; if so, engineering such systems would be difficult or even impossible. A much more powerful result would be the existence of a robust ordered phase which is characterized by the ability to perform measurement-based quantum computation. I’ll discuss some recent results on the existence of such a computational phase of matter. I’ll first outline some positive results on a phase of a toy model that contains the cluster state. Then, in a realistic model of coupled spin-1 particles, I’ll demonstrate the existence of a computational phase. This result is obtained by using a local measurement sequence to “renormalize” the state to a computationally-universal fixed point. Together, these results reveal that the characterization of computational phases of matter has a rich, complex structure – one which is still poorly understood. Joint work with Gavin Brennen, Akimasa Miyake, and Joseph Renes.
Lecture Series presented by KPMG - Quantum Foundations: From Plato's Cave to Bertlmann's Socks

Robert Spekkens Perimeter Institute for Theoretical Physics
October 25, 2009

PIRSA:09100013
Quantum Information
The mysteries of quantum theory run deep. Despite 80 years of research, there is still no consensus on its interpretation. This talk will explore some of the important issues in the foundations of quantum theory, from the idea that we have only a limited knowledge of a deeper reality, like the prisoner in Platoâs cave who sees only the shadows of objects and never the objects themselves, to John Bellâs famous discovery of the difference between quantum correlations and Dr. Bertlmannâs socks, namely, that whereas the mismatched colours of the doctorâs socks can be attributed to a decision at the sock drawer that morning, certain quantum correlations cannot be explained by a common cause, at least not without doing violence to some cherished principles of physics, such as the fact that causes cannot travel faster than the speed of light.
Harnessing Quantum Physics
- Michele Mosca Institute for Quantum Computing (IQC)
- Daniel Gottesman University of Maryland, College Park
- Dorit Aharonov Hebrew University of Jerusalem
- Ignacio Cirac Max Planck Institute for Gravitational Physics - Albert Einstein Institute (AEI)
- Peter Shor Massachusetts Institute of Technology (MIT) - Department of Mathematics
- Avi Wigderson Institute for Advanced Study (IAS)
October 18, 2009

PIRSA:09100032
Quantum Information
This panel will explore some of the deepest questions facing those who would harness the power of quantum mechanics in new quantum technologies: What are the newest and most interesting discoveries researchers have made about quantum information? What progress has been made in recent years towards experimentally harnessing quantum devices for quantum computation? What are the main motivations for building quantum information processing technologies? Drs. Aharonov and Shor appear courtesy of Institute for Quantum Computing.
Lecture Series presented by KPMG - Everyday Uses for Quantum Processors

David Cory Institute for Quantum Computing (IQC)
October 17, 2009

PIRSA:09100005
Quantum Information
Quantum computers hold the promise to revolutionize the way we secure information, compute and understand the quantum world. Although general-purpose quantum computers appear to be a long way off, we do have good test-beds of small quantum processors. One of the most versatile quantum test-beds is nuclear magnetic resonance (NMR): a version of which is familiar to many in the guise of the medical imaging modality, MRI. In fact NMR has broad importance to society: it is used in drug discovery, in oil exploration and to monitor the processing of cheese and chocolate. We will introduce NMR, show how it helps us understand quantum computing and we will look at how concepts based on quantum computing can improve NMR applications.
Adiabatic quantum optimization fails for random instances of NP-complete problems

Jeremie Roland NEC Laboratories America (Princeton)
October 07, 2009

PIRSA:09100099
Quantum Information
Adiabatic quantum optimization has attracted a lot of attention because small scale simulations gave hope that it would allow to solve NP-complete problems efficiently. Later, negative results proved the existence of specifically designed hard instances where adiabatic optimization requires exponential time. In spite of this, there was still hope that this would not happen for random instances of NP-complete problems. This is an important issue since random instances are a good model for hard instances that can not be solved by current classical solvers, for which an efficient quantum algorithm would therefore be desirable. Here, we will show that because of a phenomenon similar to Anderson localization, an exponentially small eigenvalue gap appears in the spectrum of the adiabatic Hamiltonian for large random instances, very close to the end of the algorithm. This implies that unfortunately, adiabatic quantum optimization also fails for these instances by getting stuck in a local minimum, unless the computation is exponentially long. Joint work with Boris Altshuler and Hari Krovi

Title	Speaker(s)	Date	Talk Type	Info link
A Computational Grand-Unified Theory		2010-02-03	Scientific Series	View details
Quantum Money	Scott Aaronson	2010-01-27	Scientific Series	View details
The Computational Complexity of Linear Optics	Scott Aaronson	2010-01-25	Scientific Series	View details
Random quantum satisfiability: statistical mechanics of quantum optimization	Chris Laumann	2009-12-14	Scientific Series	View details
Concentration of measure and the mean energy ensemble	Markus Müller	2009-12-07	Scientific Series	View details
Unified approach to classical and quantum dualities	Gerardo Ortiz	2009-11-18	Scientific Series	View details
Why Does Nature Like the Square Root of Negative One?	William Wootters	2009-11-18	Scientific Series	View details
Quantum computational phases of matter: measurement-based quantum computing in the Haldane phase	Stephen Bartlett	2009-11-04	Scientific Series	View details
Lecture Series presented by KPMG - Quantum Foundations: From Plato's Cave to Bertlmann's Socks	Robert Spekkens	2009-10-25		View details
Harnessing Quantum Physics	Michele Mosca, Daniel Gottesman, Dorit Aharonov, Ignacio Cirac, Peter Shor, Avi Wigderson	2009-10-18		View details
Lecture Series presented by KPMG - Everyday Uses for Quantum Processors	David Cory	2009-10-17		View details
Adiabatic quantum optimization fails for random instances of NP-complete problems	Jeremie Roland	2009-10-07	Scientific Series	View details

Quantum Information

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