Chemical Reaction Simulator on Quantum Computers by First Quantization (II)─Basic Treatment: Implementation.

Chemical simulation is a key application area that can leverage the power of quantum computers. A chemical simulator that implements a grid-based first quantization method has promising characteristics, but an implementation fully in quantum circuits seems to have not been published. Here, we present "crsQ" (chemical reaction simulator Q), which is a quantum circuit generator that generates such a chemical simulator.

Surface code for low-density qubit array.

Surface code is a promising candidate for the quantum error corrections needed for fault-tolerant quantum computations because it can operate on a two-dimensional grid of qubits. However, the gates and control lines become dense as more and more qubits are integrated, making their design and control difficult. This problem can be alleviated if the surface code can operate on sparse qubit arrays.

Continuous-variable random-number generation from an amplified spontaneous emission light source.

An amplified spontaneous emission (ASE) light source using an Er-doped fiber is an ideal random-number source in principle because ASE originates from vacuum fluctuations. Interferometrically measured ASE light directly reflects vacuum fluctuations in phase space; the interferometer does not need to be stabilized because the phase is completely random, and measurable random numbers are a continuous variable because vacuum fluctuations are continuous. These characteristics make the random-number source practical and ideal.

LD light antisqueezing through fiber propagation in reflection-type interferometer.

Antisqueezed light is a possible resource to apply quantum information technologies to the real world. When antisqueezed light is used in secure optical communications, an LD is a preferable light source from an engineering point of view. Although LD output power is low, LD light can be antisqueezed with the help of an EDFA in a reflection-type interferometer consisting of a standard single-mode fiber of typically 5 km.