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Quantum Computing
Presentation by Joe Mazzanti and Colin Hart
SRJC PHYS 43 Spring 2011
A little background…
• A computer is a programmable machine designed to sequentially
and automatically carry out a sequence of arithmetic or logical
operations.
• Conventionally a computer consists of some form of memory for
data storage, at least one element that carries out arithmetic and
logic operations, and a sequencing and control element that can
change the order of operations based on the information that is
stored.
• A computer's processing unit executes series of instructions that
make it read, manipulate and then store data.
• Historically, computers evolved from mechanical computers and
eventually from vacuum tubes to transistors. Modern computers
are usually made out of transistors made of photolithographed
semiconductors.
What is Quantum Computing?
• Definition - Use of quantum phenomenon to
perform computational operations
• Operations are done at an atomic level
Physics in Quantum Computing
• Properties employed:
– Quantum superposition
– Quantum entanglement
– Uncertainty principal
– Wave interference
Quantum based vs. Transistor based
• Bit = 0 or 1. Equivalent to switching a light
switch on and off.
• Qubit = 0 and/or 1 .
• This superposition of states is what makes
quantum computing fundamentally different.
The Bloch Sphere
• The Bloch Sphere is
a representation of a
qubit, the
fundamental building
block of quantum
computers.
Y=2n
• By performing the single operation on the qubit,
we have performed the operation on two
different values. Likewise, a two-qubit system
would perform the operation on 4 values, and a
three-qubit system on eight.
• Increasing the number of qubits therefore
exponentially increases the 'quantum parallelism'
we can obtain with the system
Heroes of Quantum Computing
•
Richard Feynman
In 1980, Richard Feynman, among others, begins to investigate the generalization of
conventional information science concepts to quantum physical processes,
considering the representation of binary numbers in relation to the quantum
states of two-state quantum systems: in other words, simulating quantum systems
not with conventional computers but with other quantum systems constructed for
this purpose.
Before we continue…
• A logic gate is an idealized or physical device
implementing a Boolean function, that is, it
performs a logical operation on one or more
logic inputs and produces a single logic
output.
Heroes of Quantum Computing
•
David Deutsch
In 1985, David Deutsch,
publishes a theoretical
paper describing a universal
quantum computer,
proving that if two-state
system could be made to evolve by means of a set of simple operations, any such
evolution could be produced, and made to simulate any physical system; these
operations come to be called quantum 'gates', as they function similarly to binary
logic gates in classical computers.
Heroes of Quantum Computing
• Peter Shor
In 1994, proposes a method using
entanglement of qubits and
superposition to find the prime
factors of an integer, a rather
valuable process as many encryption
systems exploit the difficulty in
finding factors of large numbers. In
principle, his algorithm would far
surpass the efficiency of any known
computer when executed on a
quantum computer; Shor’s discovery
proves quite instrumental in
provoking a storm of research both
by physicists and computer
scientists.
Developing Algorithms
Where are we now?
• There is active research to make computers out of
many promising new types of technology, such as:
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Optical computing
DNA computers
neural computers
quantum computers
• Some of these can easily tackle problems that modern
computers cannot.
• A 2-bit quantum computer has been made from a
thimble of chloroform; its input consists of radio
frequency pulses into the liquid containing, in essence,
the compiled program to be executed.
Applications of Quantum Computing
• Parallel computations
– Increase efficiency for iterative repetitive tasks:
• Exponential growth per qubit
• Factoring
– Cryptography
• Cracking RSA encryption
• Sorting
– Huge database management
– Identifying singularities
• Molecules, knot theory, etc.
• Game tree evaluation
• Quantum simulation
Limitations of Quantum Computing
• The Moore’s Law nano-scale conundrum:
quantum tunneling
The (De)Coherence Problem
• 1995 - The National Institute of Standards and
Technology and the California Institute of
Technology jointly contemplate the problem
of shielding a quantum system from
environmental influences and perform
experiments with magnetic fields, which allow
particles (ions) to be trapped and cooled to a
quantum state. This method, however, allows
only devices of a few bits to be created, ones
which lose coherence rapidly.
Decoherence
• Decoherence can be viewed as the loss of information from
a system into the environment (often modeled as a heat
bath). It is thus acknowledged that no system is, in reality,
perfectly isolated—but rather every system is loosely
coupled with the energetic state of its surroundings.
Viewed in isolation, the system's dynamics are nonunitary (although the combined system plus environment
evolves in a unitary fashion). Thus the dynamics of the
system alone, treated in isolation from the environment,
are irreversible. As with any coupling, entanglements are
generated between the system and environment, which
have the effect of sharing quantum information with—or
transferring it to—the surroundings.
Limitations of Quantum Computing
• Reliance on coherence
– Devolving into classical states
• Avoiding this relies on small components
• Alternatively, state can be preserved using very cold
temperatures of operation
• Very hard materials (Diamond)
Current Events
• Current method for creating qubits
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Ion Traps
Optical Traps
Quantum dots
Semiconductor impurities
Superconducting circuits
• D-Wave 16 Qubit Quantum Computer
– Demonstrated in 2010
– Solved a Sudoku Puzzle
• Qlisp- quantum programming language
Current Events
link
Predicted Growth
Q and A
Sudo.Q, anyone?
video
Resources
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http://www.doc.ic.ac.uk/~nd/surprise_97/journal/vol4/spb3/
http://www.sciam.com/1998/0698issue/0698gershenfeld.html
http://chemlinks.beloit.edu/edetc/SlideShow/images/computer/Moores_Law.jpg
http://www.youtube.com/watch?v=gKA1k3VJDq8&NR=1
http://computer.howstuffworks.com/quantum-computer1.htm
http://www.youtube.com/watch?v=HJA36PX8QOU
http://carteblancheleeway.files.wordpress.com/2010/04/s-curve.gif
http://ffden-2.phys.uaf.edu/211.web.stuff/Almeida/history.html
http://www.doc.ic.ac.uk/~nd/surprise_97/journal/vol4/spb3/#1.1 Quantum computer basics
http://dcm-workshop.org.uk./2005/dcm-draft-proceedings.pdf
http://arxiv.org/abs/quant-ph/0305025
http://en.wikipedia.org/wiki/Quantum_computer
http://en.wikipedia.org/wiki/Logic_gate#Logic_gates
http://en.wikipedia.org/wiki/Computer
http://www.sciam.com/1998/0698issue/0698gershenfeld.html