Molecular Dipolar Crystals as High Fidelity Quantum Memory for Hybrid Quantum Computing

TL;DR

This paper investigates the use of polar molecule dipolar crystals as high-fidelity quantum memories, analyzing their coherence properties, dominant decoherence mechanisms, and potential for integration with circuit QED systems.

Contribution

It provides a detailed analysis of collective excitations in dipolar molecular crystals and evaluates their suitability as quantum memories, including strategies to minimize phonon-induced decoherence.

Findings

Phonons are identified as the main decoherence source for rotational qubits.

Crystalline structure protects molecules from short-range collision effects.

Specific setups can reduce phonon coupling, enhancing qubit lifetime.

Abstract

We study collective excitations of rotational and spin states of an ensemble of polar molecules, which are prepared in a dipolar crystalline phase, as a candidate for a high fidelity quantum memory. While dipolar crystals are formed in the high density limit of cold clouds of polar molecules under 1D and 2D trapping conditions, the crystalline structure protects the molecular qubits from detrimental effects of short range collisions. We calculate the lifetime of the quantum memory by identifying the dominant decoherence mechanisms, and estimate their effects on gate operations, when a molecular ensemble qubit is transferred to a superconducting strip line cavity (circuit QED). In the case rotational excitations coupled by dipole-dipole interactions we identify phonons as the main limitation of the life time of qubits. We study specific setups and conditions, where the coupling to the phonon modes is minimized. Detailed results are presented for a 1D dipolar chain.