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in this part of the electromagnetic spectrum can effectively function
according to the laws of classical physics.
For optical wavelengths, though, photons arrive only rarely, which
makes the quantum nature of the light important. To build an optical
interferometer, one must move photonic information from one place
to another while preserving each photon’s quantum nature – exactly
the kind of task performed by quantum information researchers. Such
information generally gets lost when it travels any great distance,
limiting the resolution of current optical interferometers.
Faculty member Daniel Gottesman, IQC Faculty member Thomas
Jennewein, and Postdoctoral Researcher Sarah Croke have proposed
a way to use “quantum repeaters” to extend the distance over which
quantum information can be communicated. Quantum repeaters are
still in development, but one day, they may be incorporated into the
design of telescopes to allow observations with much higher angular
resolution than today’s best telescopes.
CAN
A
QUANTUM
COMPUTER
LEARN
FROM
ITS
MISTAKES
?
One mistake leads to another. Nowhere is this truer than in the world
of computers. Nowhere is it more difficult to deal with than in the
world of quantum computers. In a quantum system, once erroneous
information is introduced, it is nearly impossible to rectify.
There are two ways to deal with quantum computing errors. One is to
prevent them from happening in the first place, which can only be done
in very specific circumstances. The other is to build in the capacity
to correct errors as they occur. This option offers more flexibility, but
error correction on a quantum level has a difficulty that makes it akin
to magic.
One approach to building fault-tolerant quantum computers is to use
“magic states,” which contain important steps of the computation in
a separate package. A magic state is difficult to create, but once it’s
made, it can be inserted easily into any ongoing computation. Since
the magic state is self-contained, it can be tested and discarded if it
contains mistakes. Creating and comparing multiple copies of a magic
state, a process known as “distillation,” can make it possible to identify
and remove errors before they infect the main computation.
This year, a team of students and postdocs working with Associate
Faculty member Raymond Laflamme successfully achievedmagic state
distillation, an important step toward fault tolerant quantum computing.
References:
A. Miyake, “Quantum computational capability of a 2D valence bond solid phase,” Ann. Phys. 326, 1656
(2011), arXiv:1009.3491.
D. Gottesman, T. Jennewein, and S. Croke, “Longer-Baseline Telescopes Using Quantum Repeaters,”
arXiv:1107.2939.
A. M. Souza, J. Zhang, C. A. Ryan, and R. Laflamme, “Experimental magic state distillation for fault-tolerant
quantum computing,” Nature Comm. 2, 169 (2011), arXiv:1103.2178.
ASSOCIATE FACULTY
(cross-appointed with other institutions)
Niayesh Afshordi
(University of Waterloo)
Alex Buchel
(University of Western Ontario)
Cliff Burgess
(McMaster University)
Richard Cleve
(University of Waterloo)
David Cory
(University of Waterloo)
Adrian Kent
(University of Cambridge)
Raymond Laflamme
(University of Waterloo)
Sung-Sik Lee
(McMaster University)
Luis Lehner
(University of Guelph)
Michele Mosca
(University of Waterloo)
Ashwin Nayak
(University of Waterloo)
Maxim Pospelov
(University of Victoria)
Thomas Thiemann
(Max Planck Institute for Gravitational Physics)
Itay Yavin
(McMaster University)