Page 12 - 2013 Annual Report

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Chill Out, Qubits!
To err is quantum.
When wrangling the quantum building blocks of nature to perform
information processing, mistakes are bound to happen.
Quantum information is very powerful, but also very fragile.
Processors that function according to quantum laws have the
potential to be vastly more powerful than even today’s most complex
supercomputers, but the realization of that potential will hinge on
how researchers understand and deal with the errors that inevitably
arise during quantum computation.
Perimeter Faculty member Daniel Gottesman
is a pioneer in
fault-tolerant quantum computation, by which reliable computation
can happen if the error rate is kept below a given threshold.
To keep that error rate low, Gottesman and collaborators Michael
Ben-Or (Hebrew University of Jerusalem) and Avanitan Hassidim
(Bar-Ilan University) have proposed a system called a “quantum
refrigerator.”
It’s a fitting name for a proposed system that gives overheated
quantum bits (qubits) a place to chill out before being re-used for
error correction.
Quantum error correction often requires that secondary qubits –
called ancilla qubits – be utilized to measure information about errors
in a quantum computation. Typically, this measurement scrambles
the ancilla qubits, making them useful for only a single measurement.
Gottesman and collaborators, however, propose a model whereby
used ancillas are shunted into a “refrigerator” where they can cool
down, unscramble, and potentially be used again. It’s a continual
loop of heating and cooling that allows for quantum error correction
to be performed longer and more reliably than in the past.
It is, therefore, a crucial step toward stable, reliable quantum
computation – the driving motivation behind quantum information
research.
A Universal Toolkit
Of course, quantum error correction is just part of the puzzle. A
quantum computer needs stuff to compute – and stuff to compute
it with.
Quantum gates are the quantum equivalent of the logic gates in
a classical computer. They are the fundamental building blocks of
quantum circuits – the “atoms” of quantum computation, in a sense.
Quantum computers, which capitalize on quantum effects such as “superposition” and
“entanglement” to achieve processing power far surpassing present-day computers, are expected
to revolutionize how we work, communicate, and live. Much theoretical research is required,
however, before these technologies can emerge. Perimeter researchers explore quantum error
correction – the techniques needed to safeguard and verify information amid the errors inherent to
quantum computation. Researchers also pursue the foundations of quantum cryptography, which
capitalizes on uniquely quantum laws – such as the uncertainty principle – to safeguard private
information. Many of Perimeter’s quantum information researchers collaborate with scientists at
our nearby experimental partner, the Institute for Quantum Computing (IQC) at the University of
Waterloo, and some hold joint appointments at both institutes. Together, Perimeter and IQC are
transforming the region into the world’s “quantum valley.”
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Quantum Information