Aalto University researchers discovered a new and effective technique to perform interaction-free experiments. They used transmon devices, superconductive circuits exhibiting quantum behavior, to find microwave pulses that classical instruments produce. Rather than lasers and optics, the team’s lab focuses on microwaves and superconductors.
“We had to adapt the concept to the different experimental tools available for superconducting devices. Because of that, we also had to change the standard interaction-free protocol in a crucial way: we added another layer of ‘quantumness’ by using a higher energy level of the transmon. Then, we used the quantum coherence of the resulting three-level system as a resource,” Gheorghe Sorin Paraoanu said.
Quantum coherence describes how an object can occupy two states simultaneously. This complex concept may exist, but it’s delicate and could collapse. Researchers didn’t know if this protocol could work. During experimental tests, they discovered a detection efficiency increase. The team realized the discoveries stayed consistent after double-checking their results and putting their theoretical models together. “We also demonstrated that even very low-power microwave pulses can be detected efficiently using our protocol,” Shruti Dogra said.
Additionally, the experiment proved that quantum devices could achieve results that classical devices cannot reach, a quantum advantage phenomenon. Researchers think that quantum computers loaded with ample qubits could achieve a quantum advantage. However, the latest experiment demonstrates that it can occur through a simpler setup.
“Interaction-free measurements based on the earlier, less effective methodology had already noted applications in various specialized processes such as optical imaging, noise-detection, and cryptographic key distribution. This newer and better method may increase the efficiency of all those processes by a wide margin.”
“In quantum computing, our method could be applied for diagnosing microwave-photon states in certain memory elements. This can be regarded as a highly efficient way of extracting information without disturbing the functioning of the quantum processor,” Paraoanu said.
The team is also using their new technique to explore other “exotic forms of information processing.” This includes counterfactual communication (communication between two parties without transferring physical particles) and counterfactual quantum computing, which involves reaching computational results without operating the computer.