# Bit vs Qubit | Difference between Bit and Qubit (Quantum Bit)

This page compares Bit vs Qubit(Quantum Bit) and mentions difference between Bit and Qubit (Quantum Bit).

## Classical Bit

The classical logical **bit** is represented by binary logic based on either
logical high and logical low.
Logical high corresponds to binary '1' and logical low corresponds to binary '0' respectively.

The classical logical bits one and zero are represented differently in various logic families such as CMOS, TTL and ECL. This has been explained below.

For TTL, Logical '0' is represented by 0 to (1/3)(Vdd) and logical '1' is represented by (2/3)Vdd to Vdd,
Where, Vdd is supply voltage.

For CMOS, Logical '0' is represented by 0 to 0.8 V and logical '1' is represented by 2V to Vcc,
Where, Vcc is 5V+/-10%

For ECL, Logical '0' is represented by Vee to -1.4V and logical '1' is represented by -1.2V to 0V,
Where, Vee is -5.2V.

Information is represented by 0 or 1 or any combinations of 0 and 1 at a time.

## Qubit-Quantum Bit

As mentioned **Qubit** is the short form of **Quantum Bit**.
It is used in quantum computation.
A bit of data is represented by single atom which has one of the two states
designated by |0> and |1>.
Single bit of this form is referred as Qubit.

Figure-2 depicts physical implementation of Qubit which uses two energy levels of an atom to represent information. As shown excited state represents |1> and ground state represents |0>.

• NMR (Nuclear magnetic resonance) technique is used here which uses spin of an atomic nucleus to represent
Qubit.

• Chemical bonds betwen spins are manipulated using magnetic field to simulate
the gates.

Figure-1 depicts difference between Bit and Qubit.

In Qubit format, 1 "qubit" or quantum bit can represent both 0 and 1 simultaneously. Hence with 3 qubits of data, the Quantum computer can store all the 8 possible combinations of 0 and 1 simultaneously. As a result 3 Qubit based Quantum computer does calculations 8 times faster compare to 3-bit conventional computer.

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