Coping with noise in programmable quantum annealers

Sergio Boixo, Vadim Smelyanskiy, Alireza Shabani +6 more

Sergio Boixo, Tameem Albash, Federico M. Spedalieri +2 more

Marc Vuffray, Carleton Coffrin, Yaroslav A. Kharkov +1 more

Physical realizations of quantum annealers behave as samplers from Gibbs distributions with parameters that fluctuate due to noise, leading to spurious interactions between qubits in the output distributions.

Elijah Pelofske, Pratik Sathe, Cristiano Nisoli +1 more

Using programmable analog quantum annealing processors, we implement a sampling-based magnetic hysteresis protocol to probe the counterintuitive notion of magnetic memory in antiferromagnetic models. A key component of this protocol responsible for the hysteresis is a transverse field, which enables state transitions, while the longitudinal magnetic field sweep is done via a longitudinal control field. We observe intriguing non-monotonic magnetization, alongside full saturation and reversal of the hysteresis curve, Barkhausen-like noise, as well as emergent magnetic domains mediated by quantum fluctuations that give rise to the magnetic memory effect in antiferromagnets.

Steven J. Weber, Gabriel Samach, Danna Rosenberg +4 more

Sergio Boixo, Vadim Smelyanskiy, Alireza Shabani +7 more

Quantum tunnelling is a phenomenon in which a quantum state traverses energy barriers higher than the energy of the state itself. Quantum tunnelling has been hypothesized as an advantageous physical resource for optimization in quantum annealing. However, computational multiqubit tunnelling has not yet been observed, and a theory of co-tunnelling under high- and low-frequency noises is lacking. Here we show that 8-qubit tunnelling plays a computational role in a currently available programmable quantum annealer. We devise a probe for tunnelling, a computational primitive where classical paths are trapped in a false minimum. In support of the design of quantum annealers we develop a nonperturbative theory of open quantum dynamics under realistic noise characteristics. This theory accurately predicts the rate of many-body dissipative quantum tunnelling subject to the polaron effect. Furthermore, we experimentally demonstrate that quantum tunnelling outperforms thermal hopping along classical paths for problems with up to 200 qubits containing the computational primitive.