From Ultracold Molecules to Quantum Computing; Collisions Under Quantum Control

Micheline Soley University of Wisconsin-Madison

Molecules below one milliKelvin offer an unprecedented opportunity to examine chemical reactions at the level of individual quantum states and to prepare ultracold molecular qubits. A central problem in ultracold physics, which could provide new insight into the development of qubits, is how to simulate the dynamics of ultracold molecules. The long wavelengths associated with low temperatures, coupled with the exponential growth of computational cost as dimensionality increases, currently makes simulation of exact quantum dynamics of ultracold molecules cost-prohibitive for systems of more than three atoms. In addition, anomalous reflection of low-energy components of wavepackets from complex absorbing potentials (optical potentials or perfectly matching layers) has been a problem for decades in quantum scattering and time-dependent calculations, and is especially problematic in ultracold simulations given the systems’ low temperature. A solution to this problem could provide a new view into both the dynamics and control of ultracold molecular qubits. In this talk, I will present a novel method that addresses this problem based on the finding that, whereas low temperatures are typically associated with quantum mechanics, classical and semiclassical Wentzel-Kramers-Brillouin corrections can be added to complex absorbing potentials to reduce anomalous reflection by orders of magnitude. This technique offers a possible way to simulate the dynamics of ultracold molecular qubits and ultracold chemical reactions with higher accuracy and computational efficiency.

Quantum control also offers an exciting possibility to create ultracold molecular qubits by directly controlling the outcome of ultracold molecular collisions. In this talk, I will introduce a method that applies reflectionless scattering mode (RSM) theory, recently developed in optics, to direct product formation in chemical reactions with zero reformation of reactants. Surprisingly, the method only requires two variable parameters, which offers an efficient and unique approach to the creation of ultracold molecules in desired quantum states. The talk will discuss how, by combining Wentzel- Kramers-Brillouin force analysis and reflectionless scattering mode theory, one can reveal theoretically the existence of a long-sought-after fundamental physical property - PT-symmetry- breaking phenomena in fundamental quantum scattering - via standard cold-atom experiments in programmable traps.1 The talk will conclude with a discussion of quantum computing algorithms, both on quantum computers and classical computers via tensor networks/matrix product states.2,3

[1] M. B. Soley, C. M. Bender, A. D. Stone, Physical Review Letters, 130 (2023) 250404.

[2] T. H. Kyaw,* M. B. Soley,* B. Allen, P. Bergold, C. Sun, V. S. Batista, A. Aspuru-Guzik, Quantum Science and Technology, 9 (2024) 01LT01.

[3] M. B. Soley,* P. E. Videla,* E. T. J. Nibbering, V. S. Batista, Journal of Physical Chemistry Letters, 13 (2022) 8254-8263.