Hyperfine spin qubits in irradiated malonic acid: heat-bath algorithmic cooling

TL;DR

This paper demonstrates the potential of heat-bath algorithmic cooling using hyperfine spin qubits in irradiated malonic acid, showing feasibility for surpassing the Shannon bound in quantum error correction.

Contribution

It introduces a method to implement heat-bath algorithmic cooling in a 3- and 5-qubit hyperfine spin system in malonic acid, with realistic simulations indicating experimental viability.

Findings

Feasibility of cooling beyond Shannon bound in 3- and 5-qubit systems

Strong hyperfine coupling enables control of nuclei via ENDOR techniques

Simulations suggest practical implementation in molecular systems

Abstract

The ability to perform quantum error correction is a significant hurdle for scalable quantum information processing. A key requirement for multiple-round quantum error correction is the ability to dynamically extract entropy from ancilla qubits. Heat-bath algorithmic cooling is a method that uses quantum logic operations to move entropy from one subsystem to another, and permits cooling of a spin qubit below the closed system (Shannon) bound. Gamma-irradiated, $^{13}$C-labeled malonic acid provides up to 5 spin qubits: 1 spin-half electron and 4 spin-half nuclei. The nuclei are strongly hyperfine coupled to the electron and can be controlled either by exploiting the anisotropic part of the hyperfine interaction or by using pulsed electron-nuclear double resonance (ENDOR) techniques. The electron connects the nuclei to a heat-bath with a much colder effective temperature determined by the electron's thermal spin polarization. By accurately determining the full spin Hamiltonian and performing realistic algorithmic simulations, we show that an experimental demonstration of heat-bath algorithmic cooling beyond the Shannon bound is feasible in both 3-qubit and 5-qubit variants of this spin system. Similar techniques could be useful for polarizing nuclei in molecular or crystalline systems that allow for non-equilibrium optical polarization of the electron spin.