Quantum bubbles are the key

November 23, 2005

As futuristic as quantum computers seem, what with all those qubits and entangled atoms, here is an idea that promises to make atom-based quantum computers look passé even before anyone has built a full-sized version.

It seems that bubbles of electrons lined up in ultracold liquid helium could be used to build a quantum computer capable of carrying out a staggering 1030 simultaneous calculations.

To carry out these simultaneous calculations, quantum computers normally exploit entities such as atoms and molecules, which can be in several quantum states at once, to encode bits in those quantum states - the famous qubits. But Weijun Yao of Brown University in Providence, Rhode Island, wants to replace atoms with curious things called electron bubbles.

To make an electron bubble, start with liquid helium that has been cooled below 2.17 kelvin so that it behaves like a superfluid, a state of matter with zero viscosity. Now inject a fast-moving electron into the superfluid. When the electron eventually slows to a halt after numerous collisions with helium atoms, it creates a cavity about 3.8 nanometres across by repelling nearly 700 atoms' worth of helium around it (New Scientist, 14 October 2000, p 24).

It is this cavity that makes the electron bubble so very valuable. In a quantum computer, the quantum entities need to be isolated from their surroundings to preserve their fragile states. "What could be more isolated than an electron in a bubble?" asks Yao. "The electron inside each bubble interacts very weakly with the background helium atoms."

Yao says 0s or 1s could be encoded in the electrons' spins. In the presence of a magnetic field, the spin can either be parallel or anti-parallel to the field. Crucially, an electron's spin can exist in both states at the same time, enabling the qubit to be both 0 and 1.

According to Yao, large numbers of electrons, each in its own bubble, can be neatly caged using a combination of a device called a linear quadrupole trap, which traps the electrons in a line, and a set of conducting rings, which create a voltage "valley" for each bubble (see Diagram).

All the spins can be initialised to the same value by cooling the apparatus to 0.1 kelvin. You can then manipulate the electrons by applying a combination of a magnetic field gradient along the line and varying the frequency of the voltages in the quadrupole trap. This changes the spin of individual electrons and makes them interact to perform logicgate operations (www.arxiv.org/ cond-mat/0510757). To read the spin of an electron, the voltage at the end of the electron chain can be lowered so that each bubble drifts in the magnetic field gradient at a velocity that depends on the electron's spin. This drift velocity can be read using lasers.

Because each qubit carries two values, a quantum computer with two qubits could carry out four parallel calculations, one with three qubits eight calculations, and so on. "I see no major technical obstacles to the system I envisage working with 100 qubits," says Yao. "That means it could do 1000 billion billion billion operations all at once."
-end-
Written by Marcus Chown

IF REPORTING ON THIS STORY, PLEASE MENTION NEW SCIENTIST AS THE SOURCE AND, IF PUBLISHING ONLINE, PLEASE CARRY A HYPERLINK TO: http://www.newscientist.com

"This article is posted on this site to give advance access to other authorised media who may wish to quote extracts as part of fair dealing with this copyrighted material. Full attribution is required, and if publishing online a link to www.newscientist.com is also required. The story below is the EXACT text used in New Scientist, therefore advance permission is required before any and every reproduction of each article in full. Please contact celia.thomas@rbi.co.uk. Please note that all material is copyright of Reed Business Information Limited and we reserve the right to take such action as we consider appropriate to protect such copyright."

THIS ARTICLE APPEARS IN NEW SCIENTIST MAGAZINE ISSUE: 26 NOVEMBER 2005

New Scientist

Related Magnetic Field Articles from Brightsurf:

Investigating optical activity under an external magnetic field
A new study published in EPJ B by Chengping Yin, Guangdong Provincial Key Laboratory of Quantum Engineering and Quantum Materials, South China, aims to derive an analytical model of optical activity in black phosphorous under an external magnetic field.

Magnetic field and hydrogels could be used to grow new cartilage
Instead of using synthetic materials, Penn Medicine study shows magnets could be used to arrange cells to grow new tissues

Magnetic field with the edge!
This study overturns a dominant six-decade old notion that the giant magnetic field in a high intensity laser produced plasma evolves from the nanometre scale.

Global magnetic field of the solar corona measured for the first time
An international team led by Professor Tian Hui from Peking University has recently measured the global magnetic field of the solar corona for the first time.

Magnetic field of a spiral galaxy
A new image from the VLA dramatically reveals the extended magnetic field of a spiral galaxy seen edge-on from Earth.

How does Earth sustain its magnetic field?
Life as we know it could not exist without Earth's magnetic field and its ability to deflect dangerous ionizing particles.

Scholes finds novel magnetic field effect in diamagnetic molecules
The Princeton University Department of Chemistry publishes research this week proving that an applied magnetic field will interact with the electronic structure of weakly magnetic, or diamagnetic, molecules to induce a magnetic-field effect that, to their knowledge, has never before been documented.

Origins of Earth's magnetic field remain a mystery
The existence of a magnetic field beyond 3.5 billion years ago is still up for debate.

New research provides evidence of strong early magnetic field around Earth
New research from the University of Rochester provides evidence that the magnetic field that first formed around Earth was even stronger than scientists previously believed.

Massive photons in an artificial magnetic field
An international research collaboration from Poland, the UK and Russia has created a two-dimensional system -- a thin optical cavity filled with liquid crystal -- in which they trapped photons.

Read More: Magnetic Field News and Magnetic Field Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.