A research team recently presented a paper in Nature Physics describing a ground-breaking analog computer with quantum components i.e. Quantum Simulator. Created by scientists at University College Dublin (UCD) and Stanford University in the US, this device has the potential to shed light on some of the unanswered questions in physics when scaled up. 

The architecture of the new quantum gadget uses hybrid metal-semiconductor components integrated into a nanoelectronic circuit, unlike the classical computers you see in school labs. This analog design offers a means of scaling up the technology from small units to vast networks that can simulate bulk quantum matter. 

While the UCD team handled the theory and modeling, the Stanford team built and operated the device. The UCD team was led by Dr. Andrew Mitchell, Director of the UCD Center for Quantum Engineering, Science and Technology (C-QuEST) and theoretical physicist in the UCD School of Physics. The Stanford team comprises the Experimental Nanoscience Group, under the direction of Professor David Goldhaber-Gordon, and the SLAC National Accelerator Laboratory.

According to Goldhaber-Gordon, by creating a physical model of the problem instead of using computer code, analog devices offer a means to address problems. This idea is like the old mechanical model of the solar system where a crank is turned and gears simulate the movement of the planets. In the past, analog machines were used for complicated math calculations that digital computers couldn’t handle. However, the devices now need to integrate components that adhere to the laws of quantum mechanics to address quantum physics problems. In analog modeling of quantum materials, each electrical component in the circuit acts as a ‘proxy’ for an atom being simulated. While designing the new Quantum Simulator, the researchers ensured that it makes use of small electrical components that function uniformly and can be combined to create larger devices for studying bulk quantum matter. This work could lead to the creation of a new generation of scalable solid-state analog quantum computers.

“Certain problems are simply too complex for even the fastest digital classical computers to solve,” Dr. Mitchell said in a statement. For instance, scientists have been intrigued by the concept of superconductivity and wish to understand superconducting materials better. Currently, superconducting materials, which power MRI scanners and high-speed trains, only function at incredibly low temperatures. Therefore, discovering room-temperature superconducting materials using quantum simulators would be a game changer for the technology’s widespread use. However, this problem cannot be solved using existing digital computers.

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The researchers also had to make sure that the simulator was adjustable so that they could change different aspects of the experiment for better results. To their surprise, the team found most of the existing quantum simulation proposals do not meet all the requirements. Fortunately, Goldhaber-Gordon and his peers came across a solution in the work of French physicist Frédéric Pierre who was studying nanoscale devices. They discovered that the devices Pierre was studying, which were made of metal islands surrounded by electron pools, could match their requirements. These carefully designed electron pools were referred to as two-dimensional electron gases, and the flow of electrons between the pools and the metal island was controlled by voltage-controlled gates. The metal islands were essentially identical, could be tunned with electric leads, and had strong interactions with both the electrons and one another.

The team discovered that by combining the metal islands, they could build a simple system that could exhibit a quantum-critical phenomenon. They had a difficult time building the devices, but were successful eventually. The device reproduces a model of two atoms connected by an unusual quantum interaction. By tuning the electrical voltages, the researchers were able to create a new state of matter called “Z3 parafermions,” in which electrons appear to possess only a fraction of 1/3 of their usual electrical charge. These states have been touted as the foundation for future topological quantum computation, but they have never been produced using an electrical device in a lab. 

Further, their findings were identical to calculations that took weeks on a supercomputer, implying that researchers may have discovered a more effective method for studying quantum critical phenomena.

Dr. Mitchell explains the team has not built an all-purpose programmable quantum computer with sufficient power to solve all physics problems. But now, they can build analog quantum computers capable of solving some of those problems. The team hopes to create devices with more islands that can simulate large lattices of atoms, to study the behavior of real materials. Prior to this, they plan to enhance their present two-island device. First is making the metal islands smaller for better functionality at accessible temperatures. Second, instead of dropping molten metal pieces onto a semiconductor, develop a more effective approach to creating them.