Graph states, a unique class of entangled quantum states represented by graphs, have garnered significant attention in the realm of physics in recent years. Their distinctive properties have positioned them as potential game-changers in quantum computing and a variety of quantum technologies. In a canonical graph state, individual qubits are denoted by the vertices of a graph, while the entanglement between these qubits is illustrated by the edges of the graph. Moreover, the concept has been extended to include states where quantum information is stored in continuous variables, like the amplitude and phase of light.
While graph states show promise in enhancing quantum information processing and measurement tools, creating them for arbitrary graphs poses a significant challenge. It necessitates a high degree of control over the interactions that produce entanglement. Researchers at Stanford University and the SLAC National Accelerator Laboratory have made strides in this area by successfully generating continuous-variable graph states using atomic spin ensembles. Their breakthrough, published in Nature Physics, opens up a host of opportunities for leveraging these states in quantum computing and metrology systems.
For quantum computers and ultra-precise measurement tools to be practical in real-world applications, they must be both scalable and easily programmable. This entails maintaining entanglement among multiple atoms and enabling researchers to manipulate correlations within the system. The recent study by Monika Schleier-Smith, along with her graduate student Eric Cooper, focused on devising a method that is scalable and programmable for entangling atoms.
The researchers utilized advanced laser technology to control entanglement among atoms in multiple subsystems. By employing four optical tweezers to position atom clouds between mirrors, they created an optical resonator, essentially a ‘box’ that traps photons. This setup facilitated discreet information sharing between the atom clouds, leading to the emergence of entanglement. By effectively engineering a four-mode square graph state, the researchers demonstrated a scalable and efficient solution for programming entanglement between quantum nodes.
A striking revelation from the study was that a broad class of entangled states can be prepared using global interactions along with local control of individual nodes. This finding challenges the assumption that independent control over interactions between each pair of nodes is required for structuring quantum correlations. By employing global interactions akin to broadcasting messages in a social network, along with local control of nodes, the researchers were able to effectively generate complex entangled graph states.
Schleier-Smith and her research group’s work opens the door to broader applications of graph states in quantum computing and metrology. Their method has the potential to prepare entangled states tailored for specific uses, such as quantum error correction and quantum-enhanced sensing. In the short term, their focus lies on applications in quantum sensing and imaging, optimizing quantum states for recognizing spatial patterns in magnetic or optical fields. Looking ahead, they aim to extend their technique to arrays of trapped atoms serving as qubits for quantum computation, showcasing the versatility and promise of graph states in advancing quantum technologies.