Natural and magnetically induced entanglement of hyperfine-structure states in atomic hydrogen

TL;DR

This paper demonstrates that the hyperfine-structure states of atomic hydrogen can naturally exhibit and have their entanglement manipulated by magnetic fields, with potential applications in quantum information processing.

Contribution

It introduces hydrogen's hyperfine states as a fundamental quantum information resource and shows magnetic fields can induce and sustain entanglement against thermal loss.

Findings

Intrinsic entanglement decreases with temperature and vanishes above 5.35 μeV.

External magnetic fields can induce and maintain entanglement at higher temperatures.

Entanglement and coherence are expressed in terms of fundamental physical constants.

Abstract

The spectrum of atomic hydrogen has long been viewed as a Rosetta stone that bears the key to decode the writings of quantum mechanics in a vast variety of physical, chemical, and biological systems. Here, we show that, in addition to its role as a basic model of quantum mechanics, the hydrogen atom provides a fundamental building block of quantum information. Through its electron and nuclear spin degrees of freedom, the hydrogen atom is shown to lend a physically meaningful frame and a suitable Hilbert space for bipartite entanglement, whose two-qubit concurrence and quantum coherence can be expressed in terms of the fundamental physical constants -- the Planck and Boltzmann constants, electron and proton masses, the fine-structure constant, as well as the Bohr radius and the Bohr magneton. The intrinsic, natural entanglement that the hyperfine-structure (HFS) states of the H atom store at low temperatures rapidly decreases with a growth in temperature, vanishing above a $\tau_c$ $\approx$ 5.35 $\mu$eV threshold. An external magnetic field, however, can overcome this thermal loss of HFS entanglement. As one of the central findings of this work, we show that an external magnetic field can induce and sustain an HFS entanglement, against all the odds of thermal effects, at temperatures well above the $\tau_c$ threshold, thus enabling magnetic-field-assisted entanglement engineering in low-temperature gases and solids.