Memoirs of a qubit: Hybrid memory solves key problem for quantum computing

October 22, 2008

An international team of scientists has performed the ultimate miniaturisation of computer memory: storing information inside the nucleus of an atom. This breakthrough is a key step in bringing to life a quantum computer - a device based on the fundamental theory of quantum mechanics which could crack problems unsolvable by current technology.

In the quantum world, objects such as atoms are allowed to exist in multiple states simultane-ously -- that is, they could literally be in two places at once or possess a number of other seemingly mutually exclusive properties. Quantum computing is seen as the holy grail of computing because each individual piece of information, or 'bit', can have more than one value at once, as opposed to current technology which is limited to either 1s or 0s. This yields unprecedented processing power and thus dramatically widens the scope of what computers can do.

The problem: How do you isolate a quantum bit from a noisy environment to protect the deli-cate quantum information, while at the same time allowing it to interact with the outside world so that it can be manipulated and measured?

The team, with scientists and engineers from Oxford and Princeton universities and Lawrence Berkeley National Laboratory, reported a solution to this problem in the Oct. 23 issue of the journal Nature.

The team's plan was to devise a hybrid system using both the electron and nucleus of an atom of phosphorous embedded in a silicon crystal. Each behaves as a tiny quantum magnet capa-ble of storing quantum information, but inside the crystal the electron is more than a million times bigger than the nucleus, with a magnetic field that is a thousand times stronger. This makes the electron well-suited for manipulation and measurement, but not so good for storing information, which can become rapidly corrupted. This is where the nucleus comes in: when the information in the electron is ready for storage, it is moved into the nucleus where it can survive for much longer times.

The experiments were made possible by the use of silicon enriched with the single 28Si iso-tope, painstakingly grown by the Berkeley team into large crystals while keeping the material ultra-pure and free from contaminants.

"The electron acts as a middle-man between the nucleus and the outside world. It gives us a way to have our cake and eat it - fast processing speeds from the electron, and long memory times from the nucleus," said John Morton, a research fellow at St. John's College, Oxford and lead author of the Letter to Nature.

Crucially, the information stored in the nucleus had a lifetime of about 1 and 3/4 seconds, ex-ceeding a recently calculated target for quantum computing in silicon beyond which known error correction techniques could then protect the data for an arbitrarily long period of time. Without this technique the longest researchers had been able to preserve quantum information in silicon was a few tens of milliseconds.

"Nobody really knew how long a nucleus might hold quantum information in this system. With the crystals from Lawrence Berkeley and very careful measurements we were delighted to see memory times exceeding the threshold," said Steve Lyon, leader of the Princeton team.

Many different approaches to building a quantum computer are being studied, however one great advantage of the model used here is that it is based on silicon technology, which makes it more compatible with today's computers.
-end-
The work was funded in the United Kingdom by the Engineering and Physical Sciences Re-search Council and in the United States by the National Science Foundation, the National Se-curity Agency and the Department of Energy.

Notes to Editors

All the information in a normal computer is encoded in binary "bits." A bit is a fundamental unit of information, represented as a 0 or 1 in a normal digital computer. Putting lots of bits together creates a code, which generates or processes information. A quantum bit (qubit), however, could be both 1 and 0 at once. That means a single qubit has twice the power of a normal bit, but once qubits start interacting with each other the processing power increases exponentially. A system of 500 qubits represents 2500 different states (which, roughly, is 3 with 151 zeroes after it).Lawrence Berkeley National Laboratory is a U.S. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified scientific research and is managed by the University of California.

Princeton University, Engineering School

Related Quantum Computing Articles from Brightsurf:

Bringing a power tool from math into quantum computing
The Fourier transform is a mathematical operation essential to virtually all fields of physics and engineering.

New detector breakthrough pushes boundaries of quantum computing
A new paper published in Nature shows potential for graphene bolometers to become a game-changer for quantum technology

A molecular approach to quantum computing
Molecules in quantum superposition could help in the development of quantum computers.

Cosmic rays may soon stymie quantum computing
Infinitesimally low levels of radiation, such as from incoming cosmic rays, may soon stymie progress in quantum computing.

UVA pioneers study of genetic diseases with quantum computing
Scientists are harnessing the mind-bending potential of quantum computers to help us understand genetic diseases - even before quantum computers are a thing.

New method predicts spin dynamics of materials for quantum computing
Researchers at UC Santa Cruz have developed a theoretical foundation and new computational tools for predicting a material's spin dynamics, a key property for building solid-state quantum computing platforms and other applications of spintronics.

Speeding-up quantum computing using giant atomic ions
An international team of researchers have found a new way to speed up quantum computing that could pave the way for huge leaps forward in computer processing power.

Boson particles discovery provides insights for quantum computing
Researchers working on a U.S. Army project discovered a key insight for the development of quantum devices and quantum computers.

In leap for quantum computing, silicon quantum bits establish a long-distance relationship
In an important step forward in the quest to build a quantum computer using silicon-based hardware, researchers at Princeton have succeeded in making possible the exchange of information between two qubits located relatively far apart -- about the length of a grain of rice, which is a considerable distance on a computer chip.

Diversity may be key to reducing errors in quantum computing
In quantum computing, as in team building, a little diversity can help get the job done better, computer scientists have discovered.

Read More: Quantum Computing News and Quantum Computing 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.