Fundamental limitation to quantum computers

July 7, 2005

Electron microscope image of a qubit from Hans Mooij's research group at Delft University of Technology
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.

Image: Electron microscope image of a qubit from Hans Mooij's research group at Delft University of Technology.

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.

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.

Source: Netherlands Organization for Scientific Research

Explore further: Quantum sensors providing magnetic resonance with unprecedented sensitivity

Related Stories

Electronically programmable photonic molecule

December 21, 2018

Physical systems with discrete energy levels are ubiquitous in nature and form fundamental building blocks of quantum technology. Artificial atom-like and molecule-like systems were previously demonstrated to regulate light ...

Neutrinos become less and less mysterious

January 7, 2019

The authors of a study published in Physical Review D have shown that coherent neutrino scattering with nuclei provides a novel way to measure the neutrino charge radii. This interaction was theoretically predicted more ...

A two-atom quantum duet

November 9, 2018

Researchers at the Center for Quantum Nanoscience (QNS) within the Institute for Basic Science (IBS) achieved a major breakthrough in shielding the quantum properties of single atoms on a surface. The scientists used the ...

Physicists record 'lifetime' of graphene qubits

December 31, 2018

Researchers from MIT and elsewhere have recorded, for the first time, the "temporal coherence" of a graphene qubit—meaning how long it can maintain a special state that allows it to represent two logical states simultaneously. ...

Recommended for you

Archaeologists discover Incan tomb in Peru

February 16, 2019

Peruvian archaeologists discovered an Incan tomb in the north of the country where an elite member of the pre-Columbian empire was buried, one of the investigators announced Friday.

Where is the universe hiding its missing mass?

February 15, 2019

Astronomers have spent decades looking for something that sounds like it would be hard to miss: about a third of the "normal" matter in the Universe. New results from NASA's Chandra X-ray Observatory may have helped them ...

What rising seas mean for local economies

February 15, 2019

Impacts from climate change are not always easy to see. But for many local businesses in coastal communities across the United States, the evidence is right outside their doors—or in their parking lots.

The friendly extortioner takes it all

February 15, 2019

Cooperating with other people makes many things easier. However, competition is also a characteristic aspect of our society. In their struggle for contracts and positions, people have to be more successful than their competitors ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.