UPSC Prelims 2022 Q35: Where Is the Term 'Qubit' Used? — Explained
Which one of the following is the context in which the term "qubit" is mentioned?
- Cloud Services
- Quantum Computing
- Visible Light Communication Technologies
- Wireless Communication Technologies
Answer: (b) Quantum Computing
Statement-wise explanation
- a: incorrect — Cloud services rent out computing over the internet: servers, storage, platforms and software (the IaaS, PaaS and SaaS models). They run on ordinary classical hardware and store data as ordinary bits. Some providers now offer remote access to quantum machines, but the qubit belongs to that quantum hardware, not to cloud computing.
- b: correct — A qubit (quantum bit) is the basic unit of information in a quantum computer. A classical bit is either 0 or 1. A qubit can be in a superposition of 0 and 1, and several qubits can be entangled, which lets a quantum computer handle some problems far faster than a classical one. India's National Quantum Mission, approved by the Cabinet on 19 April 2023, sets its computing targets in physical qubits: 20–50 in 3 years, 50–100 in 5 years and 50–1,000 in 8 years.
- c: incorrect — Visible Light Communication sends data by switching LED light on and off very fast. Li-Fi is the best-known example. Its key terms are LEDs, photodetectors and modulation of the visible spectrum (about 400–700 nm), and it encodes data as ordinary bits. The term qubit has no role in it.
- d: incorrect — Wireless communication covers radio-based systems such as Wi-Fi, Bluetooth and 4G/5G. Its key terms are spectrum bands, MIMO antennas, bandwidth and latency, and data moves as classical bits. Quantum communication, such as quantum key distribution, is a separate field under quantum technology and is not ordinary wireless technology.
How to eliminate
You can solve this from the word itself. "Qubit" is short for "quantum bit": qu(antum) + bit. Only one option starts with the same root. The other three fields (cloud, visible light communication, wireless) all carry data as ordinary classical bits, and none uses a special unit name. In this kind of question, where you match a technical term to its field, split the term into its parts first. The fact to remember: qubit = unit of quantum information; bit = unit of classical information.
Know more
Bit vs qubit
A classical computer stores information in bits, and each bit is either 0 or 1. A quantum computer uses qubits. Two quantum effects make them different:
- Superposition: a qubit can be in a combination of 0 and 1 until it is measured. n qubits can represent 2ⁿ states at once.
- Entanglement: the states of two or more qubits become linked, so measuring one tells you about the others, however far apart they are.
The main hurdle is decoherence. Heat, vibration or stray radiation from outside disturbs qubits and causes errors ("noise"). Most machines have to be cooled close to absolute zero. Error correction combines many physical qubits into one reliable logical qubit.
| Qubit platform | Physical basis | Example |
|---|---|---|
| Superconducting | Circuits cooled near 0 K | IBM, Google |
| Trapped ion | Charged atoms held by electric fields | IonQ, Quantinuum |
| Photonic | Particles of light | PsiQuantum |
| Topological | Exotic quasiparticles (Majorana modes) | Microsoft (under debate) |
India's National Quantum Mission (NQM)
- Announced in Budget 2020 with a proposed ₹8,000 crore. The Union Cabinet approved it on 19 April 2023 with ₹6,003.65 crore for 2023-24 to 2030-31, and the Department of Science & Technology runs it.
- Computing targets: 20–50 physical qubits in 3 years, 50–100 in 5 years, 50–1,000 in 8 years.
- Four Thematic Hubs (T-Hubs): quantum computing (IISc Bengaluru), communication (IIT Madras with C-DOT), sensing and metrology (IIT Bombay), materials and devices (IIT Delhi).
- Other goals include satellite-based secure quantum communication over 2,000 km and atomic clocks for precise timing.
In the news
Budget 2020 announced a ₹8,000 crore National Mission on Quantum Technologies & Applications. In August 2021 MeitY launched India's first Quantum Computer Simulator (QSim) toolkit. Both kept quantum computing in the news before the 2022 exam.