The Indian Institute of Science (IISc) has achieved a significant milestone by developing a six-qubit photonic quantum system, the first of its kind in India and a world first for generating a six-qubit entangled GHZ (Greenberger–Horne–Zeilinger) state using gate operations without any probabilistic processes.

This system uses photons—packets of light—as qubits, leveraging their polarisation and spatial path properties to encode multiple qubits per photon. Specifically, a single photon encodes three qubits: one from polarisation and two from spatial path encoding, and by entangling two such photons, the team realised a six-qubit system.

This photonic quantum computing approach operates at room temperature and offers robustness against environmental noise, making it highly practical. The IISc team demonstrated universal quantum gates using a quantum walk mechanism with linear optical components like beam splitters and waveplates to perform deterministic multi-qubit gate operations.

This breakthrough positions India among a few nations capable of developing scalable, light-based quantum computing technologies and is part of the National Quantum Mission by the Department of Science and Technology.

A six-qubit GHZ (Greenberger–Horne–Zeilinger) state is a special type of maximally entangled quantum state involving six qubits. In this state, the qubits are linked in such a way that their individual states are not independent; rather, the entire system behaves as a single quantum entity. Formally, the six-qubit GHZ state can be written as:

This means the six qubits are either all in the state 0 or all in the state 1 simultaneously, showing perfect correlation and quantum entanglement.

For quantum computing, this is significant because the GHZ state exemplifies strong quantum correlations that enable advanced quantum phenomena such as quantum interference, teleportation, and error correction. It serves as a fundamental resource for complex quantum algorithms and protocols that outperform classical computations. Creating and manipulating such a multi-qubit entangled state demonstrates control over intricate quantum operations and is key to scaling up quantum processors.

Specifically, the IISc's achievement of generating a six-qubit GHZ state photonic system using photons and deterministic gate operations means that effective entanglement and quantum processing can be done using light-based qubits, which are robust and scalable. This enhances the prospects of building practical, scalable quantum computers capable of outperforming classical ones in specific tasks.

In summary, a six-qubit GHZ state signifies the successful control of six entangled quantum bits that can act together as a powerful computational unit, essential for advancing quantum information science and quantum technology development.​

This development is a major step towards building practical quantum computers that can eventually be widely used like classical computers, overcoming previous limitations of probabilistic photon methods by enabling deterministic qubit operations with photons.​

IDN (With Agency Inputs)