**What is a qubit and how does it differ from a classical bit?**

A qubit (or quantum bit) is the quantum mechanical analogue of a classical bit. Just as bits are the fundamental object of information in classical computing, qubits (quantum bits) are the fundamental object of information in quantum computing.

In classical computing the information is encoded in bits, where each bit can have the value zero or one.

In quantum computing the information is encoded in qubits.

Qubits can be in a state of 0 or 1 or unlike a classical bit in a linear combination (quantum superposition) of both states.

**How quantum computing is superior to traditional digital computing?**

A traditional digital computer employs binary digits, or bits, that can be in one of two states, represented as 0 and 1; thus, for example, a 4-bit computer register can hold any one of 16 (2^{4}) possible numbers.

In contrast, a quantum bit (qubit) exists in a wavelike superposition of values from 0 to 1; thus, for example, a 4-qubit computer register can hold 16 different numbers simultaneously.

In theory, a quantum computer can therefore operate on a great many values in parallel, so that a 30-qubit quantum computer would be comparable to a digital computer capable of performing 10 trillion floating-point operations per second (TFLOPS)—comparable to the speed of the supercomputers.

Quantum computing holds the promise to solve some of our planet’s biggest challenges – in the areas of environment, agriculture, health, energy, climate, materials science, and others we haven’t encountered yet.

For some of these problems, classical computing is increasingly challenged as the size of the system grows.

**How many qubits does the world’s largest quantum computer posses?**

IBM has built the largest quantum computer yet. Dubbed Osprey, it has 433 qubits, or quantum bits, which is more than triple the size of the company’s previously record-breaking 127-qubit computer and more than eight times larger than Google’s 53-qubit computer Sycamore.

**What is Quantum entanglement?**

Quantum entanglement is a phenomenon that explains how two subatomic particles can be intimately linked to each other even if separated by billions of light-years of space. Despite their vast separation, a change induced in one will affect the other.

A pair of quantum systems in an entangled state can be used as a quantum information channel to perform computational and cryptographic tasks that are impossible for classical systems.

Quantum entanglement is the phenomenon that occurs when a group of particles are generated, interact, or share spatial proximity in a way such that the quantum state of each particle of the group cannot be described independently of the state of the others, including when the particles are separated by a large distance.

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External link: https://uwaterloo.ca/institute-for-quantum-computing/quantum-101/quantum-information-science-and-technology/what-qubit

**PRACTICE QUESTIONS**

**QUES . **Which one of the following is the context in which the term “Qubit” is mentioned? **UPSC Prelims 2022**

(a) Cloud Services

(b) Quantum computing

(c)Visible light communication technologies

(d) Wireless Communication Technologies

Answer: (b) EXPLANATION: A qubit (or quantum bit) is the quantum mechanical analogue of a classical bit. In classical computing the information is encoded in bits, where each bit can have the value zero or one. In quantum computing the information is encoded in qubits. Qubits can be in a state of 0 or 1 or (unlike a classical bit) in a linear combination of both states. The name of this phenomenon is superposition. Therefore, option (b) is the correct answer.