Debasis Sadhukhan

M.Sc. Physics, IIT Bombay

1. Basics of Quantum Computation.

2.Quantum Circuits

3.Quantum Fourier Transform and it’s applications.

4.Quantum Search Algorithm

WHAT WE NEED TO KNOW

1.Basic Quantum Mechanics &

2.A little Background of Computer Science

*So, if the state can’t be written in the product state form, then they are Entangled. They are called to be Entangled State.

*Classical Analogy: No classical analog exists. But you can think of : Harry Potter and Voldemort

Examples: Bell states or EPR pairs

Some of the very important applications are :1.Super-dense coding2.Quantum Teleportation3.Quantum Cryptography4.Quantum Games

Represent a quantum state as a triangle with attached wires & do operation on quantum states just manipulating this picture

*Execution of an classical algorithm require hardware, consist of many electrical circuits containing wires and logic gates.

*These logic gates are the basic building block of a classical computer.

*Similarly, to execute a quantum algorithm we must have a quantum computer where the building blocks are quantum gates.

*So, What are the Quantum Gates…?

*As the name suggests, the gates are quantum, the laws of quantum mechanics must be applicable here.

*So, they must be unitary operator and can be made reversible.

*Note: The target and control qubit are not basis independent i.e. our target and control qubit may change if we use a different basis .

*In Classical Computation, we have seen NAND and NOR gate as universal quantum gate. A similar universality is true for quantum computation also.

*Every classical gates can be created using unitary quantum gates. In that sense quantum circuits include all the classical circuits.

*So, universality of quantum gates is obvious.

*The final state of the 1st register:

Now, apply Inverse Fourier Transform on the 1st register.

Final state:

Overall Circuit:

*The major applications are

1.Order finding

2.Prime factorization These can be used to break the

cryptosystem used in classical computer

3.Period Finding etc.

*Examples:

C:\Users\DEBASIS\Desktop\GroversQuantumSearchAlgorithm.cdf

C:\Users\DEBASIS\Desktop\SimulatedQuantumComputerAlgorithmForDatabaseSearching.cdf

*Drawback:

1.Still, the problem remains in NP class.

2.If we don’t know the exact no of solution, we may not reach to our solution as no of iteration explicitly depends on M.

References:

*[1] Michael A. Nielsen and Isaac I. Chuang, Quantum Computation and Quantum Information, Cambridge University Press(2002).

*[2] Phillip Kaye, Raymond Laflamme and Michele Mosca, An Introduction to Quantum Computing, Oxford University Press(2007).

*[3] Jamie Smith and Michele Mosca, arXiv:1001.0767v2 [quant-ph]

*[4] Lecture notes of John Preskill, California Institute of Technology: http://theory.caltech.edu/~preskill/ph229/