In a significant step towards making quantum computing practically useful on a larger scale, researchers at Oxford University Physics have achieved the first successful demonstration of distributed quantum computing. By utilizing a photonic network interface, they were able to connect two distinct quantum processors into a cohesive quantum computer, which opens doors to solving computational problems that were previously unattainable. The findings were published today (5 Feb) in Nature.
This breakthrough tackles the challenge of ‘scalability’ in quantum computing: to be truly transformative, a quantum computer would need to operate with millions of qubits. However, cramming all these processors into a singular device would necessitate an enormous machine. This innovative method involves connecting smaller quantum devices, allowing computations to be shared across a network. In theory, there’s no restriction on the number of processors that can participate in the network.
The architecture is designed around modules, each containing a limited number of trapped-ion qubits (which are the atomic-scale units of quantum information). These modules connect via optical fibers and use light (photons) instead of electrical signals for data transmission. Such photonic connections permit qubits across different modules to become entangled*, enabling quantum operations to occur across the entire network through quantum teleportation.**
While prior research has accomplished quantum teleportation of states, this study marks the first time logical gates (the essential building blocks of algorithms) have been teleported across a network. The researchers believe this could establish the foundation for a future ‘quantum internet,’ facilitating a highly secure network for communication, computation, and sensing between distant processors.
Dougal Main, the study’s lead researcher from Oxford University Physics, stated: “Previous quantum teleportation demonstrations emphasized transferring quantum states between separate systems. In our research, we apply quantum teleportation to construct interactions among these remote systems. By skillfully designing these interactions, we can carry out logical quantum gates – the core functions of quantum computing – among qubits situated in different quantum computers. This breakthrough effectively allows us to ‘connect’ various quantum processors into a singular, fully-integrated quantum computer.”
This concept is akin to the operational principles of traditional supercomputers, which are formed by linking smaller computers to achieve performance that exceeds that of individual units. This method sidesteps numerous engineering challenges linked to incorporating an ever-increasing number of qubits into a single unit, while maintaining the fragile quantum characteristics required for precise and reliable calculations.
Main further noted: “Interconnecting the modules using photonic links offers the system flexibility, enabling upgrades or replacements of modules without hindering the entire framework.”
The efficacy of this method was showcased through the implementation of Grover’s search algorithm. This quantum technique significantly accelerates the process of locating a specific item within a large, unstructured dataset, far surpassing the capabilities of conventional computers by using quantum principles like superposition and entanglement to simultaneously explore numerous possibilities. The success of this demonstration reinforces the notion that a distributed approach can enhance quantum capabilities beyond the limitations of isolated devices, paving the way for scalable, high-performance quantum computers that could perform calculations within hours that would take contemporary supercomputers years to complete.
Professor David Lucas, the lead scientist for the UK Quantum Computing and Simulation Hub guided by Oxford University Physics, remarked: “Our experiment illustrates that processing quantum information through a distributed network is something we can achieve with current technology. However, expanding quantum computers remains a significant technical hurdle, likely necessitating new scientific insights and substantial engineering efforts in the years to come.”
*Quantum entanglement: A phenomenon where two particles, such as photons, stay connected even when separated over great distances, allowing them to share information instantaneously without physical travel.
**Quantum teleportation: The process of transporting quantum information over long distances almost instantaneously by utilizing entanglement.
