Decoherence in Molecular Electron Spin Qubits: Insights from Quantum Many-Body Simulations

Abstract

Quantum states are described by wave functions whose phases cannot be directly measured, but which play a vital role in quantum effects such as interference and entanglement. The loss of the relative phase information, termed decoherence, arises from the interactions between a quantum system and its environment. Decoherence is perhaps the biggest obstacle on the path to reliable quantum computing. Here we show that decoherence occurs even in an isolated molecule although not all phase information is lost via a theoretical study of a central electron spin qubit interacting with nearby nuclear spins in prototypical magnetic molecules.The residual coherence, which is molecule-dependent, provides a microscopic rationalization for the nuclear spin diffusion barrier proposed to explain experiments. The contribution of

A reaction-coordinate perspective of magnetic relaxation

“…3). An example of this interaction occurs in Co(II) complexes, from the coupling of the magnetic nucleus of 59 Co (I ¼ 7 2…”

“…Many metal ions possess isotopes that have non-zero nuclear spin, e.g. 59 Co (I ¼ 7 2 , 100% natural abundance) or 165 Ho (I ¼ 7 2 , also 100% natural abundance). The impact of a non-zero nuclear spin is primarily observed at zero field, low temperatures, and primarily affects quantum tunneling mechanisms.…”

“…58 Existing studies place the edge of the barrier at about 3-10 Å. 57,59 However, the actual radius is dependent on the system, and does not need to be spherical. 2,60 Finally, the barrier also precludes spin diffusion as a mechanism by which the hyperfine coupling to a metal-ion nuclear spin will impact T 2 .…”

Calculating the Hyperfine Tensors for Group-IV Impurity-Vacancy Centers in Diamond: A Hybrid Density-Functional Theory Approach

“…It has been suggested that there is a barrier which we will describe by some distance r o where for 13 C nuclear spins located at distances r > r o , spin decoherence of the XV − center is produced because of entanglement, while for 13 C nuclear spins located at distances r < r o spin coherence of the XV − center is actually enhanced. [36] These two regions are separated by a barrier to spin diffusion as originally suggested by Bloembergen. [37] One interesting application of this spin diffusion barrier might be considered when we try to create a network of XV − centers in diamond experimentally.…”

Clock Transitions Guard Against Spin Decoherence in Singlet Fission

“…[15][16][17][18] Several fields in quantum measurement, from ion traps to atomic clocks and molecular magnets, take advantage of avoided crossings between various spin sublevels to dampen noise caused by fluctuating magnetic fields. 15,[18][19][20][21][22] At the avoided crossings with respect to the applied Zeeman field, transition frequencies become insensitive to field fluctuations because their first derivative with respect to the magnetic field vanishes. Transitions at these points are called "clock transitions," (CTs) because of their history in atomic clocks.…”