സൂപ്പർകണ്ടക്റ്റിംഗ് സർക്യൂട്ടുകൾ ഉപയോഗിച്ച് ക്വാണ്ടം കമ്പ്യൂട്ടിംഗിൽ വൻ കുതിച്ചുചാട്ടം: പുതിയ കണ്ടെത്തൽ

Quantum computers, computer systems that leverage the laws of quantum mechanics, store and process information using qubits (i.e., quantum bits). In many quantum computers, qubits are linked via entanglement, a quantum mechanical effect that connects particles in such a way that their shared state cannot be described as separate, independent states.

One key objective of quantum scientists is to realize entanglement between large groups of qubits. This could ultimately help to develop increasingly powerful and sophisticated quantum computers that can tackle complex optimization and computational problems.

Entanglement can be arranged into so-called graph states. The connections between qubits in these states can be described by mathematical networks, which is advantageous for quantum computation and communications.

Researchers at Tsinghua University and Hefei National Laboratory recently introduced a new strategy to link smaller entangled groups of microwave photons, individual packets of energy that make up microwave radiation, into larger, adjustable graph states. This is achieved using a circuit based on a superconductor, a material through which electrical current flows with zero electrical resistance below a specific temperature.

The team's approach, outlined in a paper published in Nature Physics, was initially used to demonstrate entanglement between 13 photonic qubits.

"Large photonic graph states are important resources for quantum communication, quantum networks and measurement-based quantum computing," Hongyi Zhang, co-senior author of the paper, told Phys.org.

"A promising way to build them is 'fusion': rather than making one very large, entangled state in a single step, one connects smaller resource states together. The difficulty is that conventional fusion methods are probabilistic, so many attempts fail and the resource overhead grows rapidly."

Building larger entangled states from small photon groups

One way to build larger graph states is via an operation called fusion, which joins smaller entangled groups of particles. Conventional fusion approaches that rely on optical components, such as mirrors and light beam splitters, do not always enable fusion, often requiring repeated attempts or additional equipment.

"We asked whether fusion could instead be made deterministic by using a quantum non-demolition measurement," explained Zhang. "Our goal was to demonstrate a deterministic, programmable fusion operation and show that it can provide a practical route to assembling larger, reconfigurable photonic graph states."

Zhang and his colleagues introduced a new approach to perform a fusion operation connecting smaller entangled states of microwave photons to produce larger graph states. Instead of preparing a large state following a single, uninterrupted process, their method essentially works by joining smaller building blocks into larger states.

"We use superconducting circuits to generate microwave photons in small, entangled states," said Zhang. "A quantum non-demolition detector then performs a parity measurement on selected photon pairs, entangling them without destroying them and thereby connecting the two smaller graph states into a larger one. Frequency tuning lets us choose which photons to fuse."

An initial demonstration and future possibilities

The fusion scheme employed by the researchers allowed them to form large graph states in which connections between qubits can be adjusted. Using their approach, the team demonstrated genuine multipartite entanglement across 13 photonic qubits, meaning the entanglement spanned the entire group rather than being confined to smaller, separate groups of photons.

"Our main contribution is a fusion operation that is deterministic, programmable and nondestructive," said Zhang. "More broadly, the work offers an architecture for scaling photonic graph states by connecting smaller, on-demand resource states. This is relevant to future measurement-based quantum computing, quantum networking and potentially quantum error-correction schemes, where both the size and the connectivity of graph states matter."

In the future, the methods introduced by these researchers could be used to realize larger and increasingly complex entangled states. Eventually, they may contribute to the advancement of quantum processors and even long-distance quantum communication networks.

"Next, we will improve the device fidelity, photon-generation efficiency and detector performance," added Zhang. "We also plan to develop multidetector architectures that can perform more fusion operations and generate larger, higher-dimensional graph states."

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