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Entangled ‘qubits’
key to quantum
By Harry Yeates,
Electronics Weekly (UK)
The prospects of building a
quantum computer using conventional
semiconductor fabrication have been improved,
thanks to work by scientists in the
US.
The researchers used
superconducting Josephson junction circuit
elements to create a system of two “entangled”
quantum bits, or qubits, in which the state of
each can be read out at the same
time.
A
qubit can exist simultaneously as both a zero
and a one, and an operation performed on an
entangled system is performed on all possible
states simultaneously.
Simultaneous readout is
crucial for a useful quantum computer, but until
now only per-qubit readout has been achieved,
since examining one qubit perturbs the state of
any others.
Robert McDermott and
colleagues at UCSB and NIST probed the energy
states of their two-qubit system by applying a
nanosecond voltage pulse and detecting tiny
changes in the magnetic field through a
transformer coil incorporated in the
qubit.
These changes were indicative
of the state of the qubit, either zero or one,
and by carefully timing the sequence of
measurement pulses, the researchers minimised
the perturbation effect. The work was published
in the journal
Science.
| 8 March 2005
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