Nanotechnology Now

Our NanoNews Digest Sponsors

Heifer International

Wikipedia Affiliate Button


Home > Press > Fundamental limitation to quantum computers

Quantum computers that store information in so-called quantum bits (or qubits) will be confronted with a fundamental limitation. This is the claim made by Dutch theoretical physicists from the Foundation for Fundamental Research on Matter (FOM) and Leiden University in an article recently published in the journal Physical Review Letters.

Fundamental limitation to quantum computers

July 07, 2005

A quantum computer can only function if the information exists for long enough to be processed. The so-called coherence of the qubit ensures that the quantum information remains intact. The researchers have now discovered that the coherence spontaneously disappears over the course of time and with this the stored information as well. This could pose a considerable problem for the development of a quantum computer.

Electron microscope image of a qubit from Hans Mooij's research group at Delft University of Technology
Electron microscope image of a qubit from Hans Mooij's research group at Delft University of Technology. Copyright Delft University of Technology.
Click image for larger version.

A quantum computer makes use of the fact that a quantum mechanical system -an electron, an atom or even a larger system such as a superconducting quantum bit - can simultaneously exist in two states. Normally one of the two states disappears as soon as the system comes into contact with the outside world. The coherence then disappears as a result of the decoherence process and the information in a quantum bit is lost.

A quantum bit typically consists of a large number of particles, with an unavoidably large number of possibilities to be influenced by the environment and thus be subjected to decoherence. Jasper van Wezel, Jeroen van den Brink (FOM) and Jan Zaanen, all attached to the Lorentz Institute of Leiden University have now investigated whether it is possible to maintain the coherence in an isolated qubit.

Much to their surprise they discovered that the coherence tends to spontaneously disappear, even without external influences. The degredation process is linked to the occurrence of quantum mechanical spontaneous symmetry breaking. In classical physics an equivalent example of this process is spontaneous crystallisation in a solution. At a certain position a crystal is spontaneously formed, as a result of which the fluid structure is broken.

According to the researchers' predictions, the coherence in some highly promising concepts for qubits will disappear after about a second. Moreover, the smaller the qubits the faster that process occurs. All of this would seem to pose a fundamental limitation on the development of qubits. Experimental research will now have to demonstrate whether this phenomenon actually occurs.


The article "An Intrinsic Limit to Quantum Coherence due to Spontaneous Symmetry Breaking" was published in Physical Review Letters, in the week ending 17 June 2005.

Dr Jeroen van den Brink
+31 (0)71 527 5510

Copyright Netherlands Organisation for Scientific Research

If you have a comment, please Contact us.

Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

Delicious Digg Newsvine Google Yahoo Reddit Magnoliacom Furl Facebook

Related Links

Foundation for Fundamental Research on Matter

Related News Press

Quantum Computing

Quantum computer coding in silicon now possible: Strongest possible proof obtained that using entanglement to write executable software code for quantum computers is indeed possible November 18th, 2015

Harris & Harris Group Portfolio Company, D-Wave Systems, Announces Multi-Year Agreement With Lockheed Martin November 16th, 2015

Los Alamos National Laboratory Orders a 1000+ Qubit D-Wave 2X Quantum Computer: Los Alamos to explore new methods of computing as part of new U.S. Government National Strategic Computing Initiative November 11th, 2015

Harris & Harris Group Portfolio Company, D-Wave Systems, Announces the Sale of Its Latest Quantum Computer to Los Alamos National Laboratory November 11th, 2015


Medical and aerospace electronics powered by Picosun ALD November 26th, 2015

Scientists design a QKD-based quantum private query with no failure November 25th, 2015

MIT mathematicians identify limits to heat flow at the nanoscale: New formula identifies limits to nanoscale heat transfer, may help optimize devices that convert heat to electricity November 25th, 2015

Physicists explain the unusual behavior of strongly disordered superconductors: Using a theory they developed previously, the scientists have linked superconducting carrier density with the quantum properties of a substance November 25th, 2015

The latest news from around the world, FREE

  Premium Products
Only the news you want to read!
 Learn More
University Technology Transfer & Patents
 Learn More
Full-service, expert consulting
 Learn More

Nanotechnology Now Featured Books


The Hunger Project

Car Brands
Buy website traffic