Transcript Quantum Computers

Quantum Computers
presented by
Siva Desaraju
Bindu Katragadda
Manusri Edupuganti
Outline
Introduction
Quantum computation
Implementation
Quantum compiler
Error correction
Architecture
Classification
Fabrication
Challenges
Advantages over classical computers
Applications
Recent advances
Timeline
Conclusion
Introduction
Quantum Mechanics
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Why? – Moore’s law
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Study of matter at atomic level (The power of atoms)
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Classical physics laws do not apply
[2]
Superposition
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Simultaneously possess two or more values
Entanglement
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Quantum states of two atoms correlated even though spatially
separated!!!
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Albert Einstein baffled “spooky action at a distance”
Bits n Qubits
Classical computers 0 or 1 (bits)
 High/low voltage
Quantum computers 0 or 1 or 0 & 1 (Qubits)
 Nuclear spin up/down 0 or 1
 Isolated atom spin up & down 0 & 1
Represent more with less (n bits 2n states)
” To be or not to be. That is the question”
– William Shakespeare
The classic answers: ”to be” or ”not to be”
[2]
The quantum answers: ”to be” or ”not to be” or
a x (to be) + b x (not to be)
Quantum Computation
Prime factorization (Cryptography)
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Peter Shor’s algorithm
Hard classical computation becomes easy quantum
computation
Factor n bit integer in O(n3)
Search an unordered list
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Lov Grover’s algorithm
Hard classical computation becomes less hard
quantum computation
n elements in n1/2 queries
Implementation model
Early quantum computation - Circuit model(ASIC)
Quantum unitary
transforms (gates)
Quantum
measurements
Quantum program
Instruction
stream
Quantum compiler
Classical bit
instruction stream
Classical
computation
Classical control
flow decisions
Quantum Compiler
Static precompiler
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End-to-end error probability
Dynamic compiler
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Accepts the precompiled binary code &
produces an instruction stream
Error Correction
Localized errors on a few qubits can have global impact
Hamming code
Difficulty of error correcting quantum states
 Classical computers – bit flip
 Quantum computers – bit flip + phase flip
 Difficulty in measurement (collapses superposition)
Quantum error correction code
 [n,k] code uses n qubits to encode k qubits of data
 Extra bits (n-k) are called ancilla bits
 Ancilla bits are in initial state
Architecture
Aims of efficient architecture
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Minimize error correction overhead
Support different algorithms & data sizes
Reliable data paths & efficient quantum
memory
Major components
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Quantum ALU
Quantum memory
Dynamic scheduler
Architecture contd…
[1]
Quantum ALU
Sequence of transforms
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the Hadamard (a radix-2, 1-qubit Fourier
transform)
identity (I, a quantum NOP)
bit flip (X, a quantum NOT)
phase flip (Z, which changes the signs of amplitudes)
bit and phase flip (Y)
rotation by π/4 (S)
rotation by π/8 (T)
controlled NOT (CNOT)
Quantum Memory
Reliable memory
Refresh units
Multiple memory banks
Quantum wires
Teleportation
Quantum swap gates
Cat state
[1]
Dynamic Scheduler
Dynamic scheduler algorithm takes
 Input - logical quantum operations,
interleaved with classical control flow
constructs
 Output - physical individual qubit operations
Uses knowledge of data size & physical qubit
error rates
Classification
Quantum Computer
Liquid Quantum Computer
Solid Quantum Computer
Si29 Doping
Phosphorous Doping
Liquid Quantum Computers
NMR Technology
Disadvantages
 Massive redundancy
 Not scalable
Solid Quantum Computers
Why silicon
Chip design aims
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Capturing & manipulating individual sub
atomic particles
Harnessing, controlling & coordinating millions
of particles at once
Si29 Doping
Need for Silicon 29 (Si29) doping
Fabrication
Advantages
Disadvantages
[9]
Phosphorous doping
[3]
Fabrication
STM technology to pluck individual atoms
from hydrogen
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PH3 used instead of P
Challenges
Decoherence
Chip fabrication
Error correction
Advantages over Classical
computers
Encode more information
Powerful
Massively parallel
Easily crack secret codes
Fast in searching databases
Hard computational problems become
tractable
Applications
Defense
Cryptography
Accurate weather forecasts
Efficient search
Teleportation
…
Unimaginable
Timeline
2003 - A research team in Japan demonstrated the first solid state
device needed to construct a viable quantum computer
2001 - First working 7-qubit NMR computer demonstrated at IBM’s
Almaden Research Center. First execution of Shor’s algorithm.
2000 - First working 5-qubit NMR computer demonstrated at IBM's
Almaden Research Center. First execution of order finding (part of
Shor's algorithm).
1999 - First working 3-qubit NMR computer demonstrated at IBM's
Almaden Research Center. First execution of Grover's algorithm.
1998 - First working 2-qubit NMR computer demonstrated at
University of California Berkeley.
1997 - MIT published the first papers on quantum computers based
on spin resonance & thermal ensembles.
1996 - Lov Grover at Bell Labs invented the quantum database
search algorithm
1995 - Shor proposed the first scheme for quantum error correction
Conclusion…will this be ever
true?
Millions into research
With a 100 qubit computer you can
represent all atoms in the universe.
If you succeed, the world will be at your
feet
[6]
References
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
http://www.cs.washington.edu/homes/oskin/Oskin-A-PracticalArchitecture-for-Reliable-Quantum-Computers.pdf
http://www.qubit.org
http://www.nature.com
http://www.wikipedia.com
http://www.howstuffworks.com
http://www.physicsweb.org/toc/world/11/3
http://www.cs.ualberta.ca/~bulitko/qc/schedule/slides/QCSS2002-06-18.ppt
http://physics.about.com/cs/quantumphysics/
http://www.trnmag.com/Stories/2002/082102/Chip_
design_aims_for_quantum_leap_082102.html
Puzzled???
"I think I can safely say that nobody understands quantum
mechanics."
- Richard P. Feynman
“Anybody who thinks they understand quantum physics
is wrong."
- Niels Bohr