3. Introduction
Superposition
Simultaneously possess two or more values
Entanglement
Quantum states of two atoms correlated even though spatially
separated!!!
Albert Einstein baffled “spooky action at a distance”
Quantum Mechanics
Why? – Moore’s law
Study of matter at atomic level (The power of atoms)
Classical physics laws do not apply
[2]
4. 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)
[2]
” To be or not to be. That is the question”
– William Shakespeare
The classic answers: ”to be” or ”not to be”
The quantum answers: ”to be” or ”not to be” or
a x (to be) + b x (not to be)
5. Quantum Computation
Prime factorization (Cryptography)
Peter Shor’s algorithm
Hard classical computation becomes easy quantum
computation
Factor n bit integer in O(n3)
Search an unordered list
Lov Grover’s algorithm
Hard classical computation becomes less hard
quantum computation
n elements in n1/2 queries
6. Implementation model
Quantum program
Quantum unitary
transforms (gates)
Quantum
measurements
Classical
computation
Classical control
flow decisions
Quantum compiler
Instruction
stream
Classical bit
instruction stream
Early quantum computation - Circuit model(ASIC)
7. Quantum Compiler
Static precompiler
End-to-end error probability
Dynamic compiler
Accepts the precompiled binary code &
produces an instruction stream
8. 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
9. Architecture
Aims of efficient architecture
Minimize error correction overhead
Support different algorithms & data sizes
Reliable data paths & efficient quantum
memory
Major components
Quantum ALU
Quantum memory
Dynamic scheduler
11. Quantum ALU
Sequence of transforms
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)
22. Advantages over Classical
computers
Encode more information
Powerful
Massively parallel
Easily crack secret codes
Fast in searching databases
Hard computational problems become
tractable
24. 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
25. 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]
27. 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
