Quantum computing

First evidence for entanglement of three macroscopic objects has been seen in a superconducting circuit built at the University of Maryland. By examining an electrical circuit operating at temperatures near absolute zero, the researchers have found new evidence that the laws of quantum mechanics apply not just to microscopic particles such as atoms and electrons, but also to large electronic devices called superconducting quantum bits (qubits).

The fastest known cryptographic system based on transmission of single photons---the smallest pulses of light---has been demonstrated by a team at the Commerce Department's National Institute of Standards and Technology (NIST). The transmissions cannot be intercepted without detection, so that messages encrypted with the system can be kept secret.

The NIST "quantum key distribution" (QKD) system transmits a stream of individual photons to generate a verifiably secret key--a random series of digital bits, each representing 0 or 1, used to encrypt messages--at a rate of 1 million bits per second (bps). This rate is about 100 times faster than previously reported systems of this type.

The demonstration, described in the May 3 issue of Optics Express,* is the first major reported result from a new NIST testbed built to demonstrate quantum communications technologies and cryptographic key distribution.

A new breed of faster, more powerful computers based on quantum mechanics may be a step closer to reality, report scientists from Purdue and Duke universities.

By linking a pair of tiny "puddles" of a few dozen electrons sandwiched inside a semiconductor, researchers have enabled these two so-called "quantum dots" to become parts of a transistor – the vital switching component in computer chips. Future computers that use quantum dots to store and process digital information might outperform conventional computer circuits because of both the new transistors' smaller size and their potential to solve problems that would take centuries on today's machines.

The quantum states of atoms and subatomic particles that prototype quantum computers use to represent the 1s and 0s of computer information are so fragile that the energy from heat, light and magnetism ordinarily found in their environments is usually enough to change them, effectively stuffing out the information they hold.

Rather than fight the odds, many researchers are working with the environmental noise to create safe havens for quantum bits, or qubits. Particles like atoms, electrons and photons can be used as qubits because they can be oriented in one of two directions -- spin up and spin down. Qubits can also be encoded in the interactions of pairs of particles. The key to making protected qubits is to encode logical qubits in multiple physical qubits.

These approaches are central to efforts aimed at making viable quantum computers, said Jason Ollerenshaw, a researcher at the University of Toronto in Canada. "Techniques for resisting environmental noise will be essential in building quantum computers on a practical scale," he said. Quantum computers hold the promise of solving certain types of problems like cracking secret codes that are far beyond the reach of ordinary computers.

Ollerenshaw and his colleagues at the University of Toronto have built a prototype quantum computer that can execute a quantum search algorithm despite environmental noise. "We have experimentally demonstrated that a quantum computer can be protected from decoherence -- the detrimental effects of environmental noise -- during the course of a complete quantum computation," said Ollerenshaw.

Researchers have overcome a major obstacle to generating random numbers on quantum computers by limiting the possibilities in the otherwise unlimited randomness of a set of quantum particles.

Random numbers play a key role in classical computing by providing an element of chance in games and simulations, a reliable method for encrypting messages, and a means of accurately sampling huge amounts of data.

Researchers from the Massachusetts Institute of Technology and the National Atomic Energy Commission in Argentina have shown that short sequences of random operations—randomly shifting laser pulses or magnetic fields—acting on a string of quantum bits can, in effect, generate random configurations of qubits.

Japan's NEC Corp and a public research body said on Thursday they had made a technological breakthrough that brought ultra-fast quantum computers a step closer.

Quantum computers, when brought into practical use, are expected to far surpass the capabilities of today's most powerful supercomputers, particularly in fields such as data mining, or searching large databases for particular pieces of information.

However, an NEC spokesman said that quantum computers for commercial use were unlikely to be available before 2020.

Quantum computers use 'qubits' -- forms of quantum particles -- as the basic information unit and these will eventually be more flexible and faster in processing information than existing computer processes.

The first element of a device that many believe holds the best hope for quantum information processing has been completed by Australian researchers, while an Austrian team has reported the first truly quantum calculation. The achievements go some way to dispelling the widely-held idea that doing anything useful with quantum computing is decades or even centuries away.

The strange properties of the quantum world should allow a quantum computer to outperform any existing computer. While classical computers process binary digits (bits) of information, quantum processors use quantum bits, or qubits, encoded in the quantum states of particles such as atoms, photons and electrons. Since such particles can be in several states at once, qubits would allow huge numbers of computations to be carried out simultaneously.

From: "Hal Finney"
To:
Sent: Saturday, August 31, 2002 1:56 PM
Subject: New algorithm for finding prime factor of large numbers

There are two known algorithms which would allow quantum computers to
threaten cryptographic systems in widespread use today. Shor's algorithm
can factor numbers and find discrete logs; and Grover's algorithm can
speed up general search problems.

Most cryptosystems in use today are hybrids, where a relatively slow
public key operation like RSA is combined with a fast symmetric algorithm
like the new AES. RSA is used to encrypt the AES key, which is then

Researchers at the University of Wisconsin in Madison claim to have created the world's first successful simulation of a quantum-computer architecture that uses existing silicon fabrication techniques. By harnessing both vertical and horizontal tunneling through dual top and bottom gates, the architecture lays out interacting, 50-nanometer-square, single-electron quantum dots across a chip.
Original article

For the first time, University of Wisconsin-Madison scientists have designed a semiconductor-based device that can trap individual electrons and line them up, an advance that could bring quantum computing out of the gee-whiz world of scientific novelty and into the practical realm.
Professors Mark Eriksson and Bob Joynt ( physics), Max Lagally (materials science and engineering), and Dan van der Weide (electrical and computer engineering) have developed a new type of "quantum dot" device for holding electrons that can be scaled up to build a working quantum computer.

Made from tiny amounts of the same semiconductor materials used in today's computer chips, each quantum dot device contains just one infinitesimally small electron. When many of the devices are aligned, the electrons they house become usable quantum bits, or qubits, for computing.