Kebiao Xu et al., have realized the adiabatic quantum factorization based on the single-spin system in diamond. This is the first time adiabatic quantum factorization has been done under ambient conditions. The research results have been accepted by Physical Review Letters.

The RSA cryptosystem is widely used for secure data transmission, such as online banking and secure network communications, the security of which is based on the practical difficulty of factoring problem. In contrast to multiplying of large prime numbers, no efficient classical algorithm for the factorization of a large number is known up to now. In 1994 Peter Shor proposed a quantum version of factorization algorithm which can accelerate the progress, and as a result, Shor’s algorithm became the driving force behind the development of quantum computing. Shor’s algorithm is based on the circuit model quantum computation, which needs a lot of qubits to factor a large number. So far, the largest number has been factored using Shor’s algorithm is 21 [Nature Photonics. 6, 773 (2012)].

In this experiment, the researchers utilized another architecture of quantum computation, i.e., the adiabatic quantum computation (AQC). AQC is a universal and robust method of quantum computing, which has been proved to be a compatible candidate for scalable quantum computation. In 2012, Du’s lab factored 143 based on an improved version of adiabatic factorization algorithm using NMR ensemble spins [Phys. Rev. Lett. 108, 130501 (2012)]. In the current work, they push it forward to realize the quantum factorization under ambient conditions with single-spins in diamond. Compared with Shor’s algorithm, adiabatic quantum factorization needs fewer quantum resource, e.g. the number 35 is factored with only two qubits. Furthermore, as a theoretical study shows, this process factors, not only 35 but also a series of integers, which can be six-digit numbers or larger [arXiv:1411.6758]. Additionally, in order to overcome the limitation of short coherence time in the ordinary diamond sample, the researchers developed optimal control pulses that can be applied to a hybrid quantum system that consists of a nuclear spin and an electronic spin.

It is possible to construct a scalable quantum processor using NV center in diamond, for example, by coupling spins in diamond or by coupling remote spins via cavity modes. As the spin system in diamond we used here is promised to reach a large scale and can work under ambient conditions, hopefully, huge numbers can be factored with this method in the future.