⚛️ Emerging Technology · Competitive Exam 2025
Quantum Computing
Complete Exam Guide
Qubits · Superposition · Entanglement · Quantum Gates · Algorithms · Hardware · India’s Quantum Mission · Threats to Cryptography · 35 MCQs — all for UPSC, SSC, IBPS, RBI, NDA & GATE
UPSC GS-IIISSC CGLIBPS PORBI Grade B
NDA/CDSGATE CSState PSCBank Internal
📋 Table of Contents
⚛️
Foundation — Start HereWhat is Quantum Computing?
Quantum Computing is a type of computing that uses the principles of quantum mechanics — the physics of subatomic particles — to process information. Unlike classical computers that use bits (0 or 1), quantum computers use qubits that can be 0, 1, or both simultaneously. This allows quantum computers to solve certain problems exponentially faster than classical computers.
⚡ Core Exam Facts
- Quantum computing is based on Quantum Mechanics (not classical mechanics or thermodynamics)
- Proposed by Richard Feynman (1981) and David Deutsch (1985)
- Classical bit = 0 or 1 | Quantum bit (qubit) = 0, 1, or both (superposition)
- NOT a faster version of classical computing — it is a fundamentally different computing paradigm
- Best suited for: cryptography, drug discovery, optimization, AI/ML, material science
- Google achieved “Quantum Supremacy” in 2019 using its Sycamore processor
⚖️
Most Asked ComparisonClassical vs Quantum Computing
💻 Classical Computing
Basic unit: Bit (0 or 1)
Processing: Sequential / parallel
Physics: Classical mechanics
Operations: Logic gates (AND, OR, NOT)
Hardware: Silicon transistors
Error rate: Very low
Temperature: Room temperature
Best for: General purpose computing
Scalability: Very high (billions of transistors)
VS
⚛️ Quantum Computing
Basic unit: Qubit (0, 1, or both)
Processing: Quantum parallelism
Physics: Quantum mechanics
Operations: Quantum gates (H, X, CNOT…)
Hardware: Superconducting circuits / trapped ions
Error rate: Very high (fragile qubits)
Temperature: Near absolute zero (−273°C)
Best for: Specific complex problems
Scalability: Very difficult (decoherence)
🔮
Most Frequently Asked — All 4 Are Exam Favourites4 Core Quantum Concepts
🎲
Qubit
The quantum equivalent of a classical bit. A qubit can be 0, 1, or a superposition of both simultaneously. Made from particles like electrons, photons, or atoms. When measured, it collapses to either 0 or 1.
Analogy
A spinning coin in the air — simultaneously “heads and tails” until you catch it (measure).
🌊
Superposition
A qubit’s ability to exist in multiple states (0 and 1) at the same time until it is measured. N qubits can represent 2ᴺ states simultaneously — enabling massive parallel computation.
Analogy
Schrödinger’s cat — both alive and dead at the same time until you open the box.
🔗
Entanglement
Two or more qubits become quantum mechanically linked — the state of one instantly determines the state of the other, regardless of distance. Einstein called this “spooky action at a distance.”
Analogy
Two magic dice always land on opposite numbers, no matter how far apart they are.
〰️
Quantum Interference
Quantum states have probability amplitudes that can add (constructive) or cancel (destructive) each other. Algorithms use this to amplify correct answers and suppress wrong ones.
Analogy
Like sound waves — two waves in sync make louder sound; out of sync cancel each other.
| Concept | What It Does | Exam One-liner | Violated By |
|---|---|---|---|
| Qubit | Stores quantum information as 0, 1, or both | Quantum version of a classical bit | Measurement (collapses state) |
| Superposition | Qubit in multiple states simultaneously | N qubits = 2ᴺ simultaneous states | Observation / measurement |
| Entanglement | Instant correlation between two qubits | Einstein: “spooky action at a distance” | Decoherence |
| Interference | Amplifies right answers, cancels wrong | Used in all quantum algorithms | Environmental noise |
| Decoherence | Loss of quantum properties due to environment | Biggest challenge in quantum computing | Temperature, vibration, radiation |
🚪
Building Blocks of Quantum AlgorithmsQuantum Gates
Quantum gates are the quantum equivalent of logic gates in classical computers. They manipulate qubits by rotating their quantum state. Unlike classical logic gates, all quantum gates are reversible. Gates are represented as unitary matrices.
H
Hadamard
Creates superposition — puts qubit into equal 0/1 probability. Most used gate.
X
Pauli-X (NOT)
Flips qubit: 0→1, 1→0. Quantum equivalent of classical NOT gate.
Z
Pauli-Z
Flips the phase of |1⟩ state. Leaves |0⟩ unchanged.
Y
Pauli-Y
Combination of X and Z gate. Rotates qubit state around Y-axis.
CNOT
Controlled-NOT
2-qubit gate: flips target qubit if control qubit is |1⟩. Creates entanglement.
T
T Gate (π/8)
Applies phase rotation of π/4. Used in universal quantum computation.
SWAP
SWAP Gate
Swaps states of two qubits. Used in routing quantum information.
Toff
Toffoli (CCNOT)
3-qubit gate — flips target if BOTH control qubits are |1⟩. Universal gate.
🎯 Gates — Exam Key Facts
- Hadamard (H) gate = most famous gate; creates superposition from a definite state
- CNOT gate = used to create entanglement between two qubits
- All quantum gates are reversible — unlike classical logic gates (AND/OR are irreversible)
- Gates are represented as unitary matrices
- A quantum circuit = sequence of gates applied to qubits (lines = qubits, boxes = gates)
- Universal gate set = {H, T, CNOT} can perform any quantum computation
🧮
Very Frequently TestedQuantum Algorithms
⚡ Shor’s Algorithm
Peter Shor — 1994
⚠️ Threatens RSA
Factorizes large integers exponentially faster than the best classical algorithms. A quantum computer with enough qubits could break RSA-2048 encryption.
Speedup: Exponential over classical | Threat: RSA, ECC, public-key cryptography
🔍 Grover’s Algorithm
Lov Grover — 1996
Quadratic Speedup
Searches an unsorted database of N items in O(√N) time vs O(N) classically. Provides quadratic (not exponential) speedup.
Speedup: √N (quadratic) | Use: Database search, password cracking faster
🧪 Deutsch-Jozsa Algorithm
Deutsch & Jozsa — 1992
First Quantum Advantage
Determines if a function is constant or balanced in one query vs 2ⁿ⁻¹+1 classically. First algorithm to prove quantum advantage.
First proof that quantum > classical | Only 1 function evaluation needed
🌡️ Quantum Simulation
Feynman’s vision — 1982
Near-term Application
Simulates quantum systems (molecules, materials) that are impossible to model on classical computers. Key for drug discovery and materials science.
Drug discovery, catalyst design, battery materials | IBM/Google leading
📈 QAOA
Farhi et al. — 2014
Optimization
Quantum Approximate Optimization Algorithm — solves combinatorial optimization problems. Used for logistics, portfolio optimization, scheduling.
Near-term quantum advantage | Finance, logistics, supply chain
🤖 Quantum ML
Emerging — 2018+
AI Enhancement
Quantum-enhanced machine learning algorithms (HHL, QSVM) that could exponentially speed up linear algebra operations underlying AI models.
HHL algorithm for linear systems | QSVM for classification
| Algorithm | Year | Problem Solved | Speedup | Real-world Impact |
|---|---|---|---|---|
| Deutsch-Jozsa | 1992 | Constant vs balanced function | Exponential | Proved quantum advantage possible |
| Shor’s | 1994 | Integer factorization | Exponential | Breaks RSA encryption |
| Grover’s | 1996 | Unsorted database search | Quadratic (√N) | Weakens symmetric encryption |
| HHL | 2009 | Linear systems of equations | Exponential (conditional) | Quantum ML, finance |
| QAOA | 2014 | Combinatorial optimization | Approximate | Logistics, scheduling |
🖥️
Frequently Asked — Know the CompaniesQuantum Hardware Technologies
🔵 Superconducting Qubits
Use Josephson junctions cooled to near absolute zero (−273°C). Fast gate operations. Currently most advanced technology for scaling.
IBM (Eagle, Osprey, Condor) · Google (Sycamore)
⚡ Trapped Ions
Use charged atoms (ions) levitated in electromagnetic traps. High fidelity but slower than superconducting. Very stable qubits.
IonQ · Honeywell Quantum Solutions · Oxford Ionics
💡 Photonic Qubits
Use photons (light particles) as qubits. Can operate at room temperature. Best for quantum communication and networking.
PsiQuantum · Xanadu · QuiX Quantum
🧲 Topological Qubits
Uses exotic quasiparticles called Majorana fermions. Inherently error-resistant. Still largely experimental but promising.
Microsoft Quantum (Azure Quantum)
⚛️ Neutral Atoms
Uses individual atoms held in optical tweezers. Scalable, programmable. Strong contender for mid-term quantum advantage.
QuEra Computing · Pasqal · Atom Computing
💎 Spin Qubits
Use electron or nuclear spin in semiconductor materials (silicon). Compatible with existing chip fabrication. Very small.
Intel · Delft University · SiQuance
🌊 Quantum Annealing
Specialised quantum optimization hardware. Not gate-based. Solves optimization by finding minimum energy state.
D-Wave Systems (Advantage processor)
☁️ Cloud Quantum
Quantum computers accessed over the internet. Democratises access to quantum hardware for researchers worldwide.
IBM Quantum Network · Amazon Braket · Azure Quantum · Google Cloud
⚡ Hardware — Exam Quick Facts
- Operating temperature: superconducting qubits need ~15 millikelvin (~−273°C, colder than outer space)
- Google Sycamore = 53 qubits → achieved quantum supremacy in 2019 (200s vs 10,000 years classically)
- IBM Condor = 1,121 qubits (2023) — largest superconducting chip
- D-Wave = world’s first commercial quantum computer (quantum annealing)
- Topological qubits (Microsoft) = most error-resistant but still research-stage
- Quantum Volume (QV) = IBM’s metric for overall quantum computer performance (not just qubit count)
🚀
Current Affairs + Exam OverlapReal-World Applications
| Domain | Application | How Quantum Helps | Example |
|---|---|---|---|
| 🔐 Cryptography | Breaking/creating encryption | Shor’s breaks RSA; QKD creates unbreakable keys | Quantum Key Distribution (QKD) |
| 💊 Drug Discovery | Molecule simulation | Simulates quantum chemistry classically impossible | Protein folding, cancer drug design |
| 💰 Finance | Portfolio optimization, risk analysis | Solves exponentially large optimization spaces | Goldman Sachs, JPMorgan research |
| 🤖 AI / ML | Faster model training | Quantum linear algebra exponentially faster | QSVM, Quantum Neural Networks |
| 🌦️ Climate / Materials | Battery, solar cell design | Simulates molecular interactions precisely | Better EV batteries, solar panels |
| 🚗 Logistics | Route optimization, supply chain | Solves Travelling Salesman Problem faster | DHL, Volkswagen, Airbus research |
| 🏦 Banking | Fraud detection, compliance | Processes complex financial datasets | HSBC, Barclays quantum pilots |
| 🔭 Space / Science | Gravitational wave detection, cosmology | Ultra-precise quantum sensors | Quantum gravimeters, atom clocks |
⚠️
UPSC GS-III / Current Affairs FavouriteQuantum Threats to Cybersecurity
🔓 Threat to RSA Encryption
Shor’s Algorithm can factor large primes exponentially faster. RSA-2048 would fall in hours/days on a sufficiently powerful quantum computer. Most internet security uses RSA.
🔓 Threat to ECC
Elliptic Curve Cryptography (used in Bitcoin, TLS, smartphones) is also vulnerable to quantum attacks via modified Shor’s algorithm.
⚡ Weakens Symmetric Encryption
Grover’s algorithm weakens AES-128 to equivalent of AES-64. Doubling key length (AES-256) remains secure — so AES-256 is considered quantum-safe.
🛡️ Post-Quantum Cryptography
NIST selected 4 post-quantum cryptographic standards in 2024: CRYSTALS-Kyber (key exchange), CRYSTALS-Dilithium, FALCON, SPHINCS+ (digital signatures).
🔑 Quantum Key Distribution (QKD)
Uses quantum mechanics to distribute encryption keys. Any interception changes the quantum state and is immediately detectable — physically unbreakable.
📡 “Harvest Now Decrypt Later”
Nation states collecting encrypted data today to decrypt once quantum computers are powerful enough. Called HNDL attack — a real current threat.
⚠️ “Q-Day” — Most Likely UPSC Topic
- “Q-Day” = predicted date when quantum computers can break RSA-2048. Estimates: 2030–2040
- NIST (US) finalised Post-Quantum Cryptography (PQC) standards in 2024
- India’s CERT-In has begun issuing quantum-readiness advisories
- QKD backbone being built in China (world’s largest, 4,600 km); India planning similar
- Quantum-safe encryption: AES-256, SHA-3 remain safe; RSA, ECC, DH are vulnerable
🇮🇳
Very High Exam Probability — 2024/2025India’s Quantum Mission (NQM)
🇮🇳 National Quantum Mission (NQM) — Approved April 2023
India approved its National Quantum Mission (NQM) in April 2023, under the Department of Science & Technology (DST), Government of India. It is India’s flagship quantum technology programme.
₹6,003 Cr
Total outlay (2023–2031)
8 Years
Duration: 2023–2031
50–1000
Target qubits by 2031
4 Hubs
Thematic Technology Hubs
| NQM Pillar | Target | Lead Institution |
|---|---|---|
| Quantum Computing | 50-qubit by 2026 → 1000-qubit by 2031 | IISc, IITs, TIFR |
| Quantum Communication | 2,000 km QKD network in India | DRDO, C-DOT, IITs |
| Quantum Sensing | Quantum clocks, gravimeters, magnetometers | NPL, ISRO, DRDO |
| Quantum Materials | New materials for qubits | IISc, JNCASR |
✅ India Quantum — Key Facts for Exam
- NQM approved by Union Cabinet in April 2023
- Nodal Ministry: Department of Science & Technology (DST)
- Budget: ₹6,003.65 crore over 8 years (2023–2031)
- 4 Thematic Technology Hubs (T-Hubs) to be set up
- India aims for 50-qubit system by 2026 and 1,000-qubit by 2031
- QKD link between Sanchar Bhavan and NIC Delhi — first QKD network in India
- ISRO developing quantum-secured satellite communications
- India is 6th country to have a dedicated national quantum mission (after USA, China, EU, UK, Canada)
🏢
Frequently Asked in Current Affairs MCQsLeading Quantum Computing Companies
| Company | Country | Key Achievement | Technology | Product/Platform |
|---|---|---|---|---|
| Google Quantum AI | USA | Quantum Supremacy (2019) — Sycamore 53 qubits | Superconducting | Sycamore, Willow (2024) |
| IBM Quantum | USA | IBM Condor — 1,121 qubits (2023) | Superconducting | IBM Q System, Quantum Network |
| Microsoft | USA | Azure Quantum, topological qubit research | Topological | Azure Quantum |
| D-Wave | Canada | First commercial quantum computer (2011) | Quantum Annealing | Advantage System |
| IonQ | USA | First publicly traded pure-play quantum company | Trapped Ions | IonQ Aria, Forte |
| Honeywell / Quantinuum | USA/UK | Highest quantum volume claims | Trapped Ions | H-Series processors |
| Rigetti | USA | Hybrid classical-quantum platform | Superconducting | Aspen processors |
| PsiQuantum | USA/Australia | Building fault-tolerant photonic QC | Photonic | Partnered with GlobalFoundries |
| China USTC | China | Jiuzhang photonic QC (2020) | Photonic / Superconducting | Zuchongzhi processor |
🎯 Company Facts — Must Know for MCQs
- Google Sycamore (2019) = first quantum supremacy claim — 53 qubits solved a problem in 200 seconds (classical: 10,000 years)
- Google Willow (2024) = new chip; solved in 5 minutes what would take classical computers 10 septillion years
- IBM Condor = 1,121 qubit processor (December 2023)
- D-Wave = first to sell a commercial quantum computer; uses quantum annealing (NOT gate-based)
- China’s Zuchongzhi = 66-qubit superconducting chip; China claims it outperforms Google Sycamore
- IonQ = first quantum company listed on NYSE stock exchange
📖
Definition-Type QuestionsKey Terms & Acronyms
| Term / Acronym | Full Form | Meaning & Exam Relevance |
|---|---|---|
| Qubit | Quantum Bit | Basic unit of quantum information; can be 0, 1, or superposition |
| QKD | Quantum Key Distribution | Secure communication using quantum mechanics; any interception is detectable |
| QEC | Quantum Error Correction | Methods to protect qubits from decoherence and noise errors |
| NISQ | Noisy Intermediate-Scale Quantum | Current era of quantum computers: 50–1000 qubits with high error rates |
| Quantum Volume | — | IBM’s metric for overall quantum computer performance (not just qubit count) |
| Quantum Supremacy | — | Quantum computer solves a problem classically practically impossible (Google, 2019) |
| Quantum Advantage | — | Quantum computer solves a USEFUL problem faster than classical (broader than supremacy) |
| Decoherence | — | Loss of quantum superposition due to environmental disturbance — main challenge |
| No-Cloning Theorem | — | Quantum states cannot be perfectly copied — basis of QKD security |
| Bra-Ket Notation | Dirac Notation | Mathematical notation for quantum states: |0⟩, |1⟩, |ψ⟩ |
| CNOT | Controlled-NOT gate | 2-qubit gate that creates entanglement; fundamental quantum gate |
| PQC | Post-Quantum Cryptography | Encryption methods safe against quantum attacks (NIST standardised 2024) |
| NQM | National Quantum Mission | India’s ₹6,003 crore quantum initiative (2023–2031) |
| QAOA | Quantum Approximate Optimization Algorithm | Near-term quantum algorithm for combinatorial optimization |
| HHL | Harrow-Hassidim-Lloyd algorithm | Quantum algorithm for solving linear systems exponentially faster |
📝
Tap Any Option to Reveal AnswerMCQ Practice — 35 Questions
What is a qubit in quantum computing?
✔ Correct: B
A qubit (quantum bit) is the basic unit of quantum information. Unlike a classical bit (0 or 1), a qubit can exist in a superposition of 0 and 1 simultaneously. When measured, it collapses to either 0 or 1.Which principle allows a qubit to exist in multiple states simultaneously?
✔ Correct: C — Superposition
Superposition allows a qubit to be in multiple states (0 and 1) simultaneously until measured. N qubits in superposition represent 2ᴺ states at once — enabling massive parallel computation.What did Einstein call quantum entanglement?
✔ Correct: B — “Spooky action at a distance”
Einstein called quantum entanglement “spooky action at a distance” — because two entangled particles instantly affect each other regardless of the distance between them, seemingly violating locality.Which quantum algorithm threatens RSA encryption by factorizing large numbers efficiently?
✔ Correct: A — Shor’s Algorithm
Shor’s Algorithm (1994, Peter Shor) can factorize large integers exponentially faster than classical computers, directly threatening RSA, ECC, and other public-key encryption systems.Grover’s algorithm is used for which purpose?
✔ Correct: B — Unsorted database search
Grover’s Algorithm (1996, Lov Grover) searches an unsorted database of N items in O(√N) time vs O(N) classically — a quadratic speedup. It weakens (but doesn’t break) symmetric encryption like AES.What is the role of the Hadamard gate?
✔ Correct: C — Creates superposition
The Hadamard (H) gate takes a definite state (|0⟩ or |1⟩) and creates an equal superposition of both — giving 50% probability for each outcome on measurement. Most fundamental quantum gate.Which quantum gate is primarily used to create entanglement between two qubits?
✔ Correct: C — CNOT gate
The Controlled-NOT (CNOT) gate entangles two qubits: it flips the target qubit if (and only if) the control qubit is |1⟩. Together with H gate, CNOT creates Bell states (maximally entangled pairs).What is the main challenge faced by quantum computers today?
✔ Correct: B — Quantum Decoherence
Quantum Decoherence — the loss of quantum superposition and entanglement due to environmental interference (heat, vibrations, electromagnetic fields) — is the biggest challenge. Qubits are extremely fragile and must be kept near absolute zero.Which company achieved “Quantum Supremacy” in 2019 using the Sycamore processor?
✔ Correct: C — Google
Google’s Sycamore (53 qubits) achieved quantum supremacy in October 2019 — completing a specific computation in 200 seconds that Google claimed would take the best classical supercomputer 10,000 years.The No-Cloning Theorem in quantum computing states that:
✔ Correct: B
The No-Cloning Theorem states that it is impossible to create a perfect copy of an unknown quantum state. This is fundamental to QKD security — any attempt to eavesdrop disturbs the quantum state and is detectable.Which field benefits MOST from quantum computing’s ability to simulate molecular interactions?
✔ Correct: B — Drug discovery and material science
Quantum computers can simulate quantum chemistry (impossible classically), enabling discovery of new drugs, catalysts, and materials. Examples: protein folding, cancer drug design, better EV battery materials.Quantum Key Distribution (QKD) is used for:
✔ Correct: B — Physically secure communication
QKD uses quantum mechanics to distribute encryption keys. Any eavesdropping attempt disturbs the quantum state and is immediately detectable — making interception physically impossible without detection.Quantum computing is based on the principles of which branch of physics?
✔ Correct: C — Quantum Mechanics
Quantum computing uses principles of Quantum Mechanics — the physics of subatomic particles, including superposition, entanglement, and wave-particle duality.India’s National Quantum Mission (NQM) was approved in which year?
✔ Correct: C — 2023 (April)
India’s National Quantum Mission (NQM) was approved by the Union Cabinet in April 2023 under the Department of Science & Technology with a budget of ₹6,003.65 crore for 2023–2031.What is the total budget of India’s National Quantum Mission?
✔ Correct: C — ₹6,003 crore
NQM budget = ₹6,003.65 crore over 8 years (2023–2031). Targets: 50-qubit system by 2026, 1,000-qubit by 2031, 4 Thematic Technology Hubs. Nodal ministry = Department of Science & Technology (DST).Which type of quantum hardware does Google use for its quantum computers?
✔ Correct: A — Superconducting qubits
Google (Sycamore, Willow) and IBM use superconducting qubits — Josephson junctions cooled to near absolute zero. IonQ uses trapped ions. Microsoft researches topological qubits. PsiQuantum uses photonic qubits.D-Wave quantum computers use which type of quantum computation?
✔ Correct: C — Quantum Annealing
D-Wave uses Quantum Annealing — a specialised technique for optimization problems. It is NOT gate-based. D-Wave produced the world’s first commercial quantum computer in 2011.What is “Quantum Supremacy”?
✔ Correct: C
Quantum Supremacy = a quantum computer solving a specific problem that would be practically impossible for the best classical supercomputer. Google’s Sycamore demonstrated this in 2019. Note: Quantum Advantage = solving a useful practical problem faster.NIST finalised Post-Quantum Cryptography (PQC) standards in which year?
✔ Correct: C — 2024
NIST (US National Institute of Standards and Technology) finalised PQC standards in August 2024. The four selected algorithms: CRYSTALS-Kyber (key exchange), CRYSTALS-Dilithium, FALCON, SPHINCS+ (digital signatures).Quantum interference in computing is used to:
✔ Correct: C
Quantum Interference exploits wave-like nature of qubits: paths leading to correct answers are constructively amplified; paths leading to wrong answers are destructively cancelled. Grover’s and Shor’s both rely on this.Who is credited with proposing the concept of quantum computing in 1982?
✔ Correct: A — Richard Feynman
Richard Feynman proposed the idea of quantum computing in 1981–1982, arguing that classical computers cannot efficiently simulate quantum systems. David Deutsch developed the first theoretical quantum computer model in 1985.NISQ stands for:
✔ Correct: B — Noisy Intermediate-Scale Quantum
NISQ describes the current era of quantum computers: 50–1,000 qubits with significant error rates (noise). We are in the NISQ era — fault-tolerant, error-corrected quantum computers are the next goal.IBM released which quantum processor with 1,121 qubits in 2023?
✔ Correct: C — IBM Condor
IBM Condor (December 2023) is a 1,121 qubit superconducting quantum processor — the world’s largest gate-based quantum processor at the time. IBM’s roadmap: Eagle (127) → Osprey (433) → Condor (1,121).Which symmetric encryption standard is considered quantum-safe?
✔ Correct: C — AES-256
Grover’s algorithm reduces AES-128 effective security to 64 bits (insufficient). AES-256 reduces to 128 bits — still considered secure. RSA-2048 is broken by Shor’s. DES is already broken classically.NQM India targets how many qubits by 2031?
✔ Correct: C — 1,000 qubits by 2031
India’s NQM roadmap: 50-qubit intermediate computer by 2026 → 1,000-qubit system by 2031. Also targets 2,000 km QKD network and 4 Thematic Technology Hubs across India.What was the significance of the Deutsch-Jozsa algorithm (1992)?
✔ Correct: B
The Deutsch-Jozsa algorithm (1992) was the first proof of quantum advantage — determining if a function is constant or balanced in ONE query vs 2ⁿ⁻¹+1 classical queries. It inspired Shor’s and Grover’s algorithms.Superconducting quantum computers operate at which extreme temperature?
✔ Correct: D — Near absolute zero
Superconducting qubits operate at ~15 millikelvin (~−273°C) — colder than outer space. This extreme cooling prevents thermal noise from disturbing the fragile quantum states (decoherence).Google’s Willow quantum chip (2024) claimed to solve in 5 minutes what would take a classical computer:
✔ Correct: C — 10 septillion years
Google’s Willow chip (December 2024) completed a benchmark computation in 5 minutes that would take the fastest classical supercomputer 10 septillion (10²⁵) years — surpassing the age of the universe.Which NIST-selected post-quantum algorithm is used for key exchange?
✔ Correct: A — CRYSTALS-Kyber
CRYSTALS-Kyber = key encapsulation mechanism (key exchange). The other three (CRYSTALS-Dilithium, FALCON, SPHINCS+) are digital signature algorithms. All four are NIST-standardised PQC algorithms (2024).The “Harvest Now Decrypt Later” (HNDL) attack refers to:
✔ Correct: B
HNDL (Harvest Now Decrypt Later) = nation-states and adversaries collecting encrypted internet traffic today, storing it, and decrypting it once quantum computers are powerful enough (Q-Day). A real and urgent current security threat.How many states can 3 qubits in superposition represent simultaneously?
✔ Correct: C — 8 states (2³)
N qubits in superposition = 2ᴺ states simultaneously. 3 qubits = 2³ = 8 states at once (000, 001, 010, 011, 100, 101, 110, 111). Compare: 3 classical bits = only 1 state at a time.NQM India is under which Ministry/Department?
✔ Correct: B — Department of Science and Technology
India’s NQM is under the Department of Science and Technology (DST), Government of India. DST oversees the 4 Thematic Technology Hubs and coordinates with IISc, IITs, DRDO, ISRO, and others.Quantum Volume (QV) is a metric developed by which company?
✔ Correct: A — IBM
Quantum Volume (QV) was developed by IBM as a more holistic benchmark than qubit count — it measures error rates, connectivity, gate fidelity, and other factors together. Higher QV = better overall performance.Which quantum computing model is specifically designed for optimization problems?
✔ Correct: C — Quantum Annealing
Quantum Annealing (used by D-Wave) is specialised for optimization problems — finding the lowest energy (optimal) configuration of a system. It is not universal gate-based quantum computing.Which of the following statements about quantum computing is INCORRECT?
✔ Correct: C — This statement is INCORRECT
Quantum computers will NOT replace classical computers for all tasks. They excel at specific problems (factorization, search, simulation, optimization) but are inefficient for everyday computing tasks (word processing, web browsing, etc.). The future is hybrid classical-quantum systems.⚡
Last-Minute PrepQuick Revision Flash Cards
⚛️ Core Concepts
- Qubit = 0, 1, or both (superposition)
- Superposition = multiple states at once
- Entanglement = “spooky action at a distance”
- Interference = amplify right, cancel wrong
- Decoherence = biggest challenge
- N qubits = 2ᴺ simultaneous states
🧮 Algorithms
- Shor’s (1994) = breaks RSA (exponential speedup)
- Grover’s (1996) = search in √N (quadratic)
- Deutsch-Jozsa (1992) = first quantum advantage
- QAOA = optimization algorithm
- HHL = linear systems solver
🚪 Key Gates
- Hadamard (H) = creates superposition
- CNOT = creates entanglement
- Pauli-X = quantum NOT (flip)
- Toffoli (CCNOT) = 3-qubit universal gate
- All gates = reversible
🏢 Companies
- Google Sycamore = quantum supremacy 2019
- Google Willow = 10 septillion year problem (2024)
- IBM Condor = 1,121 qubits (2023)
- D-Wave = 1st commercial QC (annealing)
- IonQ = 1st NYSE-listed quantum company
- Microsoft = topological qubits
🇮🇳 India NQM
- Approved: April 2023
- Ministry: DST
- Budget: ₹6,003.65 crore
- Duration: 2023–2031 (8 years)
- Target: 50-qubit (2026) → 1,000-qubit (2031)
- 4 Thematic Technology Hubs
🔐 Quantum Threats
- Shor’s breaks RSA, ECC, DH
- Grover’s weakens AES-128
- AES-256 = quantum safe
- NIST PQC: Kyber + Dilithium + Falcon + SPHINCS+ (2024)
- HNDL attack = collect now, decrypt later
- Q-Day = predicted 2030–2040
🖥️ Hardware
- Superconducting: Google, IBM
- Trapped Ions: IonQ, Honeywell
- Photonic: PsiQuantum, Xanadu
- Topological: Microsoft (research)
- Annealing: D-Wave
- Temperature: ~15 millikelvin
📖 Key Terms
- NISQ = Noisy Intermediate-Scale Quantum
- QKD = Quantum Key Distribution
- QEC = Quantum Error Correction
- PQC = Post-Quantum Cryptography
- No-Cloning = can’t copy quantum state
- Quantum Volume = IBM’s performance metric
📌 Must-Know Full Forms & Keywords
QubitNISQQEC
QKDPQCHNDL
Shor’s AlgorithmGrover’s Algorithm
CNOT GateHadamard Gate
DecoherenceQ-Day
NQM India₹6,003 crore