They are analogous to classical logic circuits but operate on qubits according to the principles of quantum mechanics.
A quantum circuit consists of a series of initializations , quantum gates measurements acting on one or more qubits in order to perform some computation.
Universality
Universality in quantum circuits is a crucial notion that refers to the ability of a set of quantum gates to approximate any quantum operation to an arbitrary degree of accuracy, similar to how classical logic gates can perform any logical operation.
A universal set of quantum gates, such as the combination of the Hadamard gate, the T gate, and the CNOT gate, enables the construction of any quantum circuit, making quantum computers flexible and scalable for a wide range of applications.
Some important circuits
Quantum Fourier Transform (QFT) Circuit:
The QFT is a crucial component in many quantum algorithms, including Shor’s algorithm for factoring integers. It transforms a quantum state into a superposition of its frequency components, enabling efficient computation of periodicity and phase estimation.
Grover’s Search Algorithm Circuit:
Grover’s algorithm is designed for searching unsorted databases, providing a quadratic speedup over classical algorithms.
The circuit involves repeated applications of a quantum oracle and amplitude amplification to increase the probability of measuring the correct solution.
Quantum Teleportation Circuit:
Quantum teleportation allows the transfer of a quantum state from one location to another without physically transmitting the particle itself.
This circuit utilizes entanglement and classical communication to achieve the transfer, demonstrating fundamental principles of quantum mechanics and enabling secure quantum communication protocols.
Challenges
Building and maintaining stable quantum circuits is challenging due to noise such as decoherence or photon loss, which can easily disrupt quantum states. Error correction techniques used in FTQC are crucial for mitigating these issues.