# Introduction to Quantum Computing

## Applications

• Game design
• Quantum Chemistry to calculate bond lengths between atoms

## Coding

`from qiskit import *qr = QuantumRegister(2)cr = ClassicalRegister(2)circuit = QuantumCircuit(qr,cr)circuit.draw()`

To build entanglements, we need gates… Hadamard gates.

`circuit = circuit.h(qr)circuit.draw(output='mp1')`

Controlled X like logical if. Say here control is qr and the target is qr

`circuit.cx(qr,qr)`

Measure the qubits, take those bits and store in classical bits

`circuit.measure(qr,cr)   #qr=>cr`

Simulate the circuit locally using `Aer`

` simulator = Aer.simulate('qasm-simulator')`

Execute the circuit which returns results

`result = execute(circuit,backend=simulator).result()`

Visualize

`from qiskit.tools.visualization import plot_histogramplot_histogram(result.get_counts(circuit))`

Place on Quantum Computer and test

`from qiskit import IBMQIBMQ.save('...')IBMQ.load_account()provider = IBMQ.get_provider('ibm-q')qcomp = provider.get_backend('ibmq_16_melbourne')job =  execute(circuit,backend=qcomp)`

The job is placed on Qcomp but it doesn't execute immediately. Others might be using the same Qcomp, so it may take time to return. We can monitor the job by job_monitor

`from qiskit.tools.monitor import job_monitorjob_monitor(job)result = job.result()`

## Different ways people discuss the quantum state:

1. Bracket representation — state vector simulator
2. Gates can be represented as matrices and operations on it are operations on vectors — unitary simulator
3. Bloch sphere (visual representation of state) — state vector simulator
4. How circuit works as a result of measurement — qasm simulator

[1 0] is state 0> [0 1] is state 1> [0 1, 1 0] is state of X

# Quantum Algorithms

## Quantum Teleportation:

When we want to copy one qbit info to another, simple copy results in change measurement destroy the state. We take help of entanglement for quantum teleportation.

## Bernstein Vazirani Algorithm:

Quantum computer can guess a secret number of n bits in one shot which takes n shots in classical computer.

--

--