Record entanglement, secure worldwide communications and quantum error correction at upcoming meeting

Washington, DC, June 7, 2001---Two revolutions of the 20th century--the information explosion and the quantum theory of submicroscopic matter--are poised to create a new revolution in the 21st century, one that may lead to faster computers, unbreakable codes, and new forms of communication.

Researchers from around the world will present the latest progress in these areas at the first International Conference on Quantum Information (ICQI), scheduled to take place from June 10-13, 2001 at the University of Rochester campus in Rochester, New York. The primary sponsors of the conference are the Optical Society of America and the University of Rochester's Institute of Optics and the Department of Physics and Astronomy.

Introduction

In this age of the World Wide Web, word processors, and other abundant sources of data, it's tempting to think of information as an abstract commodity that can be perfectly copied and distributed to others without limit. But the very idea of information itself is being sharpened and expanded as scientists explore a new frontier, one that promises powerful breakthroughs that would make our current computer technology look primitive. As these scientists realize, information is not a philosophical abstraction but a concrete entity that is manipulated through physical processes. In the past decade researchers have investigated how data can be stored in single atoms, photons, electrons, and other particles that play by the bizarre rules of quantum mechanics.

Quantum Computers--Traditional or "classical" computers read, write, and store data in binary terms: Each bit of data is either a 0 or 1. In a quantum computer, a bit of data could exist as a 0 AND 1 at the same time. Stringing together many of these quantum bits, or "qubits," a large-scale quantum computer would be able to perform a staggering number of calculations in parallel. Because of this massively parallel behavior, quantum computers could crack existing security codes in a short amount of time, and search astronomically large databases exponentially faster than the best supercomputer today. That's because quantum computers would manipulate and process information in individual submicroscopic particles such as atoms. Such particles have the unusual ability to exist in two or more different energy states simultaneously, each of which can represent a 0 and 1 at the same time. Only the smallest quantum computers, consisting of a few qubits, currently exist, and they perform trivial calculations. Constructing a large-scale quantum computer is a major challenge, and some believe that one may never be built, because the slightest disturbance can cause the computer to crash. Building from the ground up, researchers are nonetheless finding innovative solutions, such as "quantum error correction," which can fix data corrupted by outside influences.

Quantum Cryptography--Particles at the quantum scale can produce the most secure encryption codes imaginable to humankind. They would be impervious even to quantum computers. In "quantum cryptography," one creates special "entangled" pairs of subatomic particles such as photons (particles of light), and sends one particle of each pair to a message sender and receiver. Each particle represents either a 0 or 1. The value of an individual particle is randomly determined, but it has a definite relationship with its partner particle. Many such particle pairs would be transmitted to sender and receiver, forming a random string of digits known only to sender and receiver. Next, the sender converts the intended message to binary code, and then adds the message to the random string to form a new random string of numbers. The receiver reads the message just by subtracting the key. Because of the particle's "entangled" nature, any eavesdropper's attempt to intercept the random code will alter it in a detectable way, enabling the users to discard the appropriate parts of the data. Simple forms of quantum cryptography have been demonstrated over relatively short distances, but researchers are working to bring the technique to a practical stage.

Other Quantun Information Applications--Special properties of the quantum world have many other potential applications. For example, "quantum lithography" may enable researchers to create computer circuits with smaller features than allowed by the classical laws of physics, by taking advantage of light's special quantum properties, which enables it to create smaller patterns than nature allows. "Quantum communication" enables people to send information more efficiently, saving time and energy. Other, completely unimagined applications of quantum information are possible.

Meeting Highlights Here are descriptions of some of the many interesting papers to be delivered at the meeting:

The Largest Entanglement Ever

Entanglement has been for a long time considered one of the most profound features of quantum mechanics. In 1935 Einstein, Podolsky, and Rosen (EPR) published a famous paper formulating what they perceived as a paradox created by quantum mechanics. The EPR paradox for two particles, as stated by EPR themselves, was that a measurement of the position or momentum on one particle immediately and non-destructively reveals the position or momentum for the other particle, even if the two were completely separated from each other. This demonstrated what Einstein called "spooky action at a distance." It has been generally believed that entanglement manifests itself only in systems consisting of a small number of microscopic particles. Contrary to this belief, Eugene Polzik and his colleagues at Aarhus University in Denmark, 011-45-89423745, polzik@ifa.au.dk have experimentally demonstrated the entanglement of two macroscopic gases each consisting of about 10 billion atoms. These are by far the largest objects entangled in a laboratory "on demand." Besides the fundamental interest, the robust, long-lived entanglement of material objects demonstrated here is expected to play an important role in quantum information processing, including quantum memory and ultra-precise measurements. (Paper QECCA4, Tuesday, 11:30AM-12:00PM.)

Toward Secure Communication Worldwide Quantum key distribution (QKD) cryptography is a highly secure technique for exchanging keys that unlock secret communiques. By generating a random number and transmitting it via specially prepared trains of individual photons, one person can send another a cryptographic key with absolute confidence that no one else as has intercepted it - any attempt to eavesdrop on the key exchange would mix the photons in a way that would both reveal the eavesdropper's presence and scramble the key.

Laboratory demonstration of QKD is relatively easy, but reliably transmitting individual photons over the distances necessary for secure communications in the real world presents significant technological challenges. Richard Hughes hughes@lanl.gov, 505-667-3876 and colleagues at the Los Alamos National Laboratory are developing techniques to exchange quantum keys using photons transmitted through the atmosphere over distances of up to 1.6 kilometers, even in poor weather conditions and the optically noisy environment of broad daylight. The development could ultimately lead to satellite-based key distribution and absolutely secure communications on a global scale. (Paper QECCB1, Tuesday, 9:30-10:00 AM.)

Debugging Quantum Data Information can be either analog (the hands of an analog clock can point in any direction) or digital (the readout of a digital clock advances in discrete jumps). This distinction exists even for data stored in individual particles at the quantum level. An electron in free space can be at any position -- it carries analog quantum information. An electron bound in an atom can be at any of a discrete set of atomic energy states -- it carries digital quantum information. Fixing errors in quantum information is essential for making a properly working quantum computer. Five years ago, schemes were invented for protecting digital quantum information from errors. Now, Daniel Gottesman (UC Berkeley), Alexei Kitaev (Microsoft Research), and John Preskill (Caltech, 626-395-6691, preskill@theory.caltech.edu) have come up with a method for suppressing errors in analog quantum information.

The solution is important because some types of analog quantum information, such as quantum states of light, are particularly easy to manipulate accurately in the laboratory. Preskill and his colleagues will describe how a robust quantum computation could be executed by processing such states. The computation can be carried out with tools that are plausibly available in the laboratory of a quantum optician. Preprint at http://xxx.lanl.gov/abs/quant-ph/0008040. (Tutorial T3, Tuesday, 8:30-9:30 AM.)

Other Topics Here are some of the other topics to be discussed at the meeting: quantum data hiding (Barbara Terhal, IBM); an entangled photon laser (D. Bouwmeester, Oxford); automated design of quantum circuits (Colin Williams, Stanford); the cost of communication (Benjamin Schumacher, Kenyon); the binding force of an optics "molecule" (EJS Fonseca, Univ. Federal de Minas Gerais, Brazil); experimental realization of a Shor-type quantum algorithm (Isaac Chuang, MIT); superconducting qubits meets Schrodinger's cat (James Lukens, SUNY Stony Brook); contemplating quantum computation (David Mermin, Cornell).

These items were prepared by Ben Stein and James Riordon of the American Institute of Physics in cooperation with the Optical Society of America and the respective speakers. ---------------------------------------------------------------------------

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ICQI Meeting, June 10-13, 2001
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