Quantum simulator

In this photograph of a quantum simulator crystal the ions are fluorescing, indicating the qubits are all in the same state (either "1" or "0"). Under the right experimental conditions, the ion crystal spontaneously forms this nearly perfect triangular lattice structure. Credit: Britton/NIST
Quantum simulator illustration: The heart of the simulator is a two-dimensional crystal of beryllium ions (blue spheres in the graphic); the outermost electron of each ion is a quantum bit (qubit, red arrows). The ions are confined by a large magnetic field in a device called a Penning trap (not shown). Inside the trap the crystal rotates clockwise. Credit: Britton/NIST

Quantum simulators permit the study of quantum systems that are difficult to study in the laboratory and impossible to model with a supercomputer. In this instance, simulators are special purpose devices designed to provide insight about specific physics problems.[1][2][3]

Solving physics problems

A trapped-ion simulator, built by a team that included the NIST and reported in April 2012, can engineer and control interactions among hundreds of quantum bits (qubits). Previous endeavors were unable to go beyond 30 quantum bits. As described in the scientific journal Nature, the capability of this simulator is 10 times more than previous devices. Also, it has passed a series of important benchmarking tests that indicate a capability to solve problems in material science that are impossible to model on conventional computers.

Furthermore, many important problems in physics, especially low-temperature physics, remain poorly understood because the underlying quantum mechanics is vastly complex. Conventional computers, including supercomputers, are inadequate for simulating quantum systems with as few as 30 particles. Better computational tools are needed to understand and rationally design materials, such as high-temperature superconductors, whose properties are believed to depend on the collective quantum behavior of hundreds of particles.[2][3]

The trapped-ion simulator

The trapped-ion simulator consists of a tiny, single-plane crystal of hundreds of beryllium ions, less than 1 millimeter in diameter, hovering inside a device called a Penning trap. The outermost electron of each ion acts as a tiny quantum magnet and is used as a qubit, the quantum equivalent of a “1” or a “0” in a conventional computer. In the benchmarking experiment, physicists used laser beams to cool the ions to near absolute zero. Carefully timed microwave and laser pulses then caused the qubits to interact, mimicking the quantum behavior of materials otherwise very difficult to study in the laboratory. Although the two systems may outwardly appear dissimilar, their behavior is engineered to be mathematically identical. In this way, simulators allow researchers to vary parameters that couldn’t be changed in natural solids, such as atomic lattice spacing and geometry. In the NIST benchmarking experiments, the strength of the interactions was intentionally weak so that the simulation remained simple enough to be confirmed by a classical computer. Ongoing research uses much stronger interactions.[2][3]

Quantum simulation

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 exponentially with the number of qubits: 2N states for N qubits.[4][5]

Crucially, the simulator can also engineer a second quantum property called entanglement between the qubits, so that even physically well separated particles may be made tightly interconnected.[2][3][4]

See also

References

  1. ↑ Johnson, Tomi H.; Clark, Stephen R.; Jaksch, Dieter (2014). "What is a quantum simulator?". EPJ Quantum Technology 1 (10). doi:10.1186/epjqt10.
  2. ↑ 2.0 2.1 2.2 2.3  This article incorporates public domain material from the National Institute of Standards and Technology document "NIST Physicists Benchmark Quantum Simulator with Hundreds of Qubits" by Michael E. Newman (retrieved on 2013-02-22).
  3. ↑ 3.0 3.1 3.2 3.3 Britton, Joseph W.; Sawyer, Brian C.; Keith, Adam C.; Wang, C.-C. Joseph; Freericks, James K.; Uys, Hermann; Biercuk, Michael J.; Bollinger, John J. (2012). "Engineered two-dimensional Ising interactions in a trapped-ion quantum simulator with hundreds of spins". Nature 484 (7395): 489–92. arXiv:1204.5789. Bibcode:2012Natur.484..489B. doi:10.1038/nature10981. PMID 22538611. Note: This manuscript is a contribution of the US National Institute of Standards and Technology and is not subject to US copyright.
  4. ↑ 4.0 4.1 Cirac, J. Ignacio; Zoller, Peter (2012). "Goals and opportunities in quantum simulation". Nature Physics 8 (4): 264. Bibcode:2012NatPh...8..264C. doi:10.1038/nphys2275.
  5. ↑ Nature Physics Insight – Quantum Simulation. Nature.com. April 2012.