(SEM VII) THEORY EXAMINATION 2022-23 QUANTUM COMPUTING

SECTION A (2 Marks Each)

(a) Father of Quantum Computing

Richard Feynman is considered the father of Quantum Computing.

(b) Difference between Bit and Qubit

A bit can be either 0 or 1, while a qubit can be 0, 1, or a superposition of both at the same time.

(c) Quantum Gates: Reversible or Irreversible

Quantum gates are reversible in nature.

(d) Conditions for Quantum Computation

The main conditions are superposition, entanglement, coherence, and unitary operations.

(e) Nuclear Magnetic Resonance (NMR)

NMR is a technique that uses magnetic fields to study atomic nuclei and is used to implement qubits in quantum computing.

(f) Can Quantum Computers Become Self-Aware?

No, quantum computers cannot become self-aware because they lack consciousness and emotions.

(g) One Characteristic of Markov Process

The future state depends only on the present state, not on past states.

(h) Any Three Quantum Operations

Hadamard operation, Pauli-X operation, and CNOT operation.

(i) Shannon Entropy: Positive or Negative

Shannon entropy is always positive or zero.

(j) Shor Code

Shor code is a quantum error-correcting code that protects qubits from bit-flip and phase-flip errors.

SECTION B (10 Marks Each – Any Three)

(a) Interest in Quantum Computers and Quantum Simulators

Quantum computers are of great interest today because they can solve complex problems much faster than classical computers. They are especially useful in cryptography, material science, drug discovery, optimization, and simulation of quantum systems. Quantum simulators help researchers study systems that are impossible to simulate using classical computers, making them highly valuable in modern research.

(b) Hurdles in Developing Quantum Computers

The main challenges include maintaining qubit stability, controlling quantum decoherence, error correction, scalability, and extremely low temperature requirements. Quantum systems are highly sensitive to noise and environmental disturbances, which makes practical implementation difficult.

(c) Entanglement in Quantum Computing

Entanglement is a quantum phenomenon where two or more qubits become linked such that the state of one qubit directly affects the state of the other, even if they are far apart. It is a key resource for quantum speed-up, teleportation, and quantum communication.

(d) Quantum Electrodynamics (QED) and Its Importance

Quantum electrodynamics is the theory that describes how light and matter interact at the quantum level. It is important in quantum computing because it helps in understanding photon-based qubits and quantum interactions in electromagnetic fields.

(e) Error Correction in Quantum Computing

Quantum error correction protects quantum information from errors caused by noise and decoherence. For example, Shor’s code encodes one logical qubit into multiple physical qubits to detect and correct errors without directly measuring the quantum state.

SECTION C (10 Marks Each)

Q3 (a) Three Key Attributes to Measure Quantum Computer Performance

The three key attributes are number of qubits, quantum coherence time, and gate fidelity. These determine the power, stability, and reliability of a quantum computer.

Q3 (b) Classical Computing vs Quantum Computing

Classical computing uses bits that operate as 0 or 1, while quantum computing uses qubits that can exist in superposition. Quantum computers can process multiple possibilities simultaneously and solve certain problems exponentially faster than classical computers.

Q4 (a) Universal Quantum Gates

Universal quantum gates are a set of gates that can be combined to perform any quantum computation. Examples include Pauli gates, Hadamard gate, Phase gate, and CNOT gate. These gates manipulate qubits through unitary operations.

Q4 (b) Searching an Unstructured Database (N/2 Classical Limit)

In classical computing, searching an unstructured database requires checking on average N/2 elements. Quantum algorithms like Grover’s algorithm reduce this complexity to √N, showing quantum advantage.

Q5 (a) Working of Photon Quantum Computers

Photon quantum computers use photons as qubits. Information is encoded in properties like polarization or phase of photons. These systems operate at room temperature and are suitable for quantum communication.

Q5 (b) Types of Quantum Computers

The three types are Superconducting quantum computers, Trapped ion quantum computers, and Photonic quantum computers. Each uses different physical systems to represent qubits.

Q6 (a) Problems Best Suited for Quantum Computing

Quantum computing is best suited for problems involving factorization, optimization, cryptography, quantum simulation, and large database searching.

Q6 (b) Quantum Noise in Digital Images

Quantum noise appears as random variations in pixel intensity due to quantum fluctuations. It affects image clarity and is significant in low-light imaging systems.

Q7 (a) Quantum Error Correction Code

Quantum error correction codes protect quantum information by encoding logical qubits into multiple physical qubits to detect and correct errors without collapsing the quantum state.

Q7 (b) Stabilizer Code

Stabilizer codes are a class of quantum error-correcting codes that use stabilizer operators to detect errors efficiently. Shor code and Steane code are examples.