Analog quantum computers developed by researchers at UCD (University College of Dublin) and Stanford University could solve some of the most exciting unanswered questions in quantum physics. The essential idea behind these specialised analog devices is to build a hardware solution to the problem rather than writing code for a digital computer. The new ‘quantum simulator’ architecture involves electronic circuits with nanoscale components whose properties are governed by the laws of quantum mechanics.
These components can be fabricated, and importantly, behave essentially identically to each other – allow for the analog simulation of quantum materials, where each electronic component in the circuit acts as a proxy for an atom being simulated.
Eventually, Goldhaber-Gordon said, the team hopes to build devices with more and more islands, so that they can simulate larger and larger lattices of atoms, capturing essential behaviors of real materials.
First, they are hoping to improve the design of their two-island device. One aim is to decrease the size of the metal islands, which could make them operate better at accessible temperatures: cutting-edge ultralow temperature “refrigerators” can reach temperatures down to a fiftieth of a degree above absolute zero, but that was barely cold enough for the experiment the researchers just finished. Another is to develop a more reliable process for creating the islands than essentially dripping molten bits of metal onto a semiconductor.
The researchers believe, their work could lay the foundation for significant advances in physicists’ understanding of certain kinds of superconductors and perhaps even more exotic physics, such as hypothetical quantum states that mimic particles with only a fraction of the charge of an electron.
Tuning a material to the cusp between two distinct ground states can produce physical properties that are unlike those in either of the neighbouring phases. Advances in the fabrication and control of quantum systems have raised the tantalizing prospect of artificial quantum simulators that can capture such behaviour. A tunable array of coupled qubits should have an appropriately rich phase diagram, but realizing such a system with either tunnel-coupled semiconductor quantum dots or metal nanostructures has proven difficult. The challenge for scaling up to clusters or lattices is to ensure that each element behaves essentially identically and that the coupling between elements is uniform, while also maintaining tunability of the interactions. Here we study a nanoelectronic circuit comprising two coupled hybrid metal–semiconductor islands, combining the strengths of both materials to form a potentially scalable platform. The semiconductor component allows for controllable inter-site couplings at quantum point contacts, while the metal component’s effective continuum of states means that different sites can be made equivalent by tuning local potentials. The couplings afforded by this architecture can realize an unusual quantum critical point resulting from frustrated Kondo interactions. The observed critical behaviour matches theoretical predictions, verifying the success of our experimental quantum simulation.
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