Cryptography Watch

NEC, JST and RIKEN successfully demonstrate world’s first controllably coupled qubits
Newly developed circuit technology enables execution of quantum algorithm

Tokyo, May 3, 2007–NEC Corporation, Japan Science and Technology Agency (JST) and the Institute of Physical and Chemical Research (RIKEN) have together successfully demonstrated the world’s first quantum bit (qubit) circuit that can control the strength of coupling between qubits. Technology achieving control of the coupling strength between qubits is vital to the realization of a practical quantum computer, and has been long awaited in the scientific field.

The quantum computer, when it is finally brought to fruition, is expected to far surpass the capabilities of even the most modern of today’s supercomputers. Actual computing in a quantum computer is carried out by manipulating the quantum state of qubits in time sequence by external controls. To achieve such manipulation, it is necessary to control the: 1. States of individual qubits, 2. States of two qubits (logic operation), and 3. Ability to turn on /off the coupling between qubits.

NEC, JST, and RIKEN have already announced successful development of key technologies for the world’s first solid-state qubit and the world’s first two-qubit logic gate, based on solid-state technology that excels in its ability to integrate qubits. Following these achievements, the research group addressed the controllable coupling of qubits as the next logical step in realization of a practical quantum computer. Their new research result represents the world’s first successful demonstration of controllably coupled qubits.

To date, the coupling of qubits has been difficult to control. In order to realize this control, the research group devised an original mechanism that employs another qubit in between the two qubits for coupling. The coupling qubit functions as a non-linear transformer that is able to turn on and off the magnetic coupling between the two qubits, and on/off control is achieved simply by inputting a microwave. Moreover, coupling operation has been achieved without shortening the lifetime of each qubit. Scalability is also realized through the repetition of coupled two-qubit units - a feature necessary for future quantum computers.

To demonstrate the operation feasibility of the controllable coupling scheme, the research group employed a coupled two-qubit system, the smallest quantum logic unit, to carry out a multi-quantum control experiment involving the turning on and off of the coupling. As a result, a simple quantum protocol has been successfully demonstrated, allowing controllable coupling for the execution of quantum algorithms.

In the near future, NEC, JST, and RIKEN, plan to implement a larger-scale, more elaborate quantum computation, aiming for the realization of a practical quantum computer.

The result of this joint research will be published in the May 4th issue of the international weekly science journal, Science, published by the American Association for the Advancement of Science (AAAS).

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Paper Title: Quantum Coherent Tunable Coupling of Superconducting Qubits

A part of this research has been carried out under the following JST project:

* Project Name: Core Research for Evolutional Science and Technology (CREST)
* Research Area: “Creation of New Technology Aiming for the Realization of Quantum Information Processing Systems” (Research
* Supervisor: Professor Yoshihisa Yamamoto, National Institute of Informatics / Stanford University)
* Research Theme: “Superconducting Qubit System”
* Research Director: Jaw-Shen Tsai, Fellow, NEC Nano Electronics Research Laboratories / Laboratory Head, Riken Frontier Research System
* Research Period: 2003 to 2008

NEC PRESS CONTACTS

Japan

Diane Foley
d-foley@ax.jp.nec.com
+81-3-3798-6511 Asia Pacific

Masako Hirano
m-hirano@bccs.nec.com.sg
+65-63792570

Europe

Chris Shimizu
chris.shimizu@uk.neceur.com
+44-20-8752-2794

America

Kazuko Andersen
Kazuko.Andersen@necam.com
+1- 212-326-2502

RIKEN PRESS CONTACT

Public Relations Office
RIKEN
+81-48-467-9272

JST PRESS CONTACT

Mikiko FUKUSHIMA
Public Relations Division
Japan Science and Technology Agency
+81-3-5214-8404

ChannelNews Asia reports that Singapore has announced a S$150m in funds for a Quantum Computation research center to be located at the National University of Singapore. The research center will be called the Research Centre of Excellence on Quantum Information Science and Technology, or QIST.

Statements senior Singaporian officials indicate that the center will work on Quantum Communication and Quantum Cryptography. Specifically, on communication systems which make use of the Heisenberg Uncertainty Principle to preclude tapping. Professor Ekert, Director of the Research Centre of Excellence, suggested that the motivation behind the creation of the center was partially to provide domestically manufactured versions of such communications systems. The validation testing of secure communications devices can be difficult, problematic, and expensive.

The high level of recent interest in Quantum Communication Technology may indicate that the technology is nearing a level of development which will allow for widespread application. MIT has recently announced a Quantum Computation research center and scientists at MIT have been examining the security of Quantum Communication Devices, like those developed by BBN.

The Massachusetts Institute of Technology has announced that The Keck Foundation has funded a major new center for Quantum Information Theory. The new W. M. Keck Foundation Center for Extreme Quantum Information Theory (xQIT) will focus of the research areas of adiabatic quantum computing; quantum channel capacity; and quantum sensing and control.

Researchers have demonstrated Shor’s Quantum Factoring Algorithm experimentally on a 4bit number[1]. Researchers were able to use the algorithm to determine the factors of the number 15, 3 and 5.

[1] Vandersypen, L. M. K., Steffen, M., Breyta, G., Yannoni, C. S., Sherwood, M. H., Chuang, I. L. Experimental realization of Shor’s quantum factoring algorithm using nuclear magnetic resonance, Nature 414, 883-887 (2001).

Abstract
The number of steps any classical computer requires in order to find
the prime factors of an l-digit integer N increases exponentially with l, at
least using algorithms known at present. Factoring large integers is therefore
conjectured to be intractable classically, an observation underlying the security
of widely used cryptographic codes. Quantum computers, however, could factor
integers in only polynomial time, using Shor’s quantum factoring algorithm.
Although important for the study of quantum computers, experimental
demonstration of this algorithm has proved elusive. Here we report an
implementation of the simplest instance of Shor’s algorithm: factorization
of N = 15 (whose prime factors are 3 and 5). We use seven spin-1/2
nuclei in a molecule as quantum bits, which can be manipulated with
room temperature liquid-state nuclear magnetic resonance techniques.
This method of using nuclei to store quantum information is in principle
scalable to systems containing many quantum bits, but such scalability
is not implied by the present work. The significance of our work lies in
the demonstration of experimental and theoretical techniques for precise
control and modeling of complex quantum computers. In particular, we
present a simple, parameter-free but predictive model of decoherence
effects in our system.

Peter Shor {W} has published a paper which describes a polynomial time factorization algorithm[1].

Shor, Peter W. Polynomial-Time Algorithms for Prime Factorization and Discrete Logarithms on a Quantum Computer, SICOMP Volume 26 Issue 5 pp. 1484-1509, 1997.*

Abstract:

A digital computer is generally believed to be an efficient universal computing
device; that is, it is believed able to simulate any physical computing device with an
increase in computation time of at most a polynomial factor. This may not be true
when quantum mechanics is taken into consideration. This paper considers factoring
integers and finding discrete logarithms, two problems which are generally thought
to be hard on a classical computer and have been used as the basis of several
proposed cryptosystems. Efficient randomized algorithms are given for these two
problems on a hypothetical quantum computer. These algorithms take a number
of steps polynomial in the input size, e.g., the number of digits of the integer to
be factored.

* Reference updated to reflect revised draft.