Developers ofquantum computersshould give up on
the familiar 1s-and-0s binary system used in conventional
computers. By switching to a novel five-state system, they will
find it easier to build the staggeringly powerful
machines.
So claim
Matthew
Neeley and colleagues at the University of California, Santa
Barbara (UCSB).
So far, the development of quantum computers has followed the
traditional binary computing model. This encodes all information
using components that can be in two states, either 1 or 0.
But other possibilities exist, Neeley explains. "We could use a
'trinary' system with three digits - 0, 1 and 2 - and then the
fundamental units would be trinary digits, or trits, that would
essentially be three-position switches." A single "trit" would
contain more information a conventional "bit".
Neeley's team have now built a quantum computer whose building
blocks have five basic states.
Five-state system
Until now, quantum computers' basic components have been binary
quantum bits - qubits - which encode two states in the quantum spin
of atoms, electrons or photons. The ability of such particles to
defy everyday logic, and exist in multiple quantum states at once,
should one day enable quantum computers to perform vast numbers of
calculations simultaneously.
Neeley's group used a superconducting aluminium and silicon
circuit on a sapphire wafer to make five-state qubits, or "qudits",
that operate at 0.025 kelvin.
"There's more information stored in a qudit than a qubit, so a
given computation can be done with fewer qudits," Neeley told New
Scientist.
By firing microwave photons of five different frequencies into
the circuit, they were able to encourage it to jump between five
discrete energy levels. "We also developed a quantum measuring
technique that can distinguish between all of these levels," says
Neeley.
Simultaneous existence
Because, in probabilistic terms, the qudit's five quantum states
are able to exist simultaneously, the team had a working qudit on
their hands.
One qudit alone is of little use, however.
Jonathan Home at the US
National Institute of
Standards and Technology in Boulder, Colorado, says Neeley's
team needs to extend its basic system in such a way that two or
more qudits can transport information between them, which would
allow more complex computational operations to be undertaken.
"Designing the sort of system where two qudits interact, but
still retain the interesting properties of a five-level system,
will be a major challenge," Home says.
Quantum spies
The potential power of quantum computers means has attracted the
interest of the US
Intelligence Advanced
Research Projects Agency (IARPA), which hopes to use them to
break codes.
Home's team has received funding from the agency to work on a
room-temperature quantum computer that allows binary qubits to
interact and swap information.
Their latest results show that magnesium ions can be used to
stop the qubits destabilising one another by transferring heat as
well as their quantum states.
The trick, reported in this week's Science
(
DOI: 10.1126/science.1177077) is to use serried ranks of
trapped beryllium ions as the qubits, while using neighbouring
magnesium ions to absorb any heat. The heat would normally destroy
quantum information as it is transported between them.
"This will pave the way to large-scale quantum computing,
because it addresses the major task: information transport," says
Home.
Journal reference:
Science, DOI: 10.1126/science.1173440