An international group of scientists, working with the National Institute for Science and Technology (NIST) in the US have built the world’s largest ever quantum simulator, smashing previous record for the number of qubits. The device, which has passed a series of benchmarking tests, could be used to simulate problems in quantum mechanics that would be utterly intractable for a conventional computer.
The scientists collected three hundred beryllium ions in a device called a Penning Trap, creating a two dimensional grid. The qubits in the simulator are the magnetic spins of the outermost electron of each ion.
To check whether or not the crystal would work, the scientists had to devise a simple simulation whose results could be checked on a classical computer. Using lasers, they cooled the crystal to near-absolute zero, before poking at it with precisely controlled and timed pulses of microwave and laser. This triggered interactions between the qubits that successfully modelled quantum behaviour.
"The projected performance of this new experimental quantum simulator eclipses the current maximum capacity of any known computer by an astonishing 10 to the power of 80. That is 1 followed by 80 zeros, in other words 80 orders of magnitude, a truly mind-boggling scale," Dr Michael Biercuk, at the University of Sydney, said. "[It] has the potential to perform calculations that would require a supercomputer larger than the size of the known universe - and it does it all in a diameter of less than a millimetre."
From the NIST announcement: Simulators exploit a property of quantum mechanics called superposition, wherein a quantum particle is made to be in two distinct states at the same time, for example, aligned and anti-aligned with an external magnetic field. So the number of states simultaneously available to 3 qubits, for example, is 8 and this number grows exponential with the number of qubits: 2N states for N qubits.
Crucially, the NIST simulator also can engineer a second quantum property called entanglement between the qubits, so that even physically well separated particles may be made tightly interconnected.
"Many properties of natural materials governed by the laws of quantum mechanics are very difficult to model using conventional computers. The key concept in quantum simulation is building a quantum system to provide insights into the behaviour of other naturally occurring physical systems," Biercuk continues.
He likens the quantum simulator to a wind tunnel; a scaled down version of something that can give insights into real-world behaviour and interactions.
"By engineering precisely controlled interactions and then studying the output of the system, we are effectively running a 'program' for the simulation. In our case, we are studying the interactions of spins in the field of quantum magnetism - a key problem that underlies new discoveries in materials science for energy, biology, and medicine."
The work was carried out by researchers at the University of Sydney, in collaboration with South Africa’s Council for Scientific and Industrial Research in South Africa, Georgetown University in Washington and North Carolina State University. It is published in the April 26 edition of the journal Nature.