Low-field dephasing time of an optically polarized NV- spin bath beyond the P1 limit in diamond: a cluster-correlation-expansion and exact spin-bath study
Abstract
Dense ensembles of nitrogen-vacancy (NV-) centres in nitrogen-rich diamond dephase on the electron spins of the substitutional nitrogen (P1) centres. If the paramagnetic nitrogen is instead converted into NV- centres, the laser that initializes the sensor also pumps the bath into ms = 0, a state with no moment along its own axis. Using cluster-correlation-expansion (CCE) calculations, combined with an exact solver for probe-bath exchange and with no adjustable parameter, this paper asks whether such an optically polarized NV- bath dephases a sensor more slowly than a P1 bath of the same density. The answer is set by the field. In a field along [111], three quarters of the bath centres lie off the field axis, and the moment of their ms = 0 state along the field grows from 0.04 at 25 G to 0.46 at 300 G and 0.81 at 800 G. At 25 G the polarized bath is therefore nearly silent: at 1017 cm−3 the dephasing time T2* of a separately addressed 15NV- probe is 112 us, six times the 18.1 us of a P1 bath, and still 2.4 times at 90 % polarization; an ensemble measurement gains a factor of two. At 300 G the advantage over P1 shrinks to 1.4, and at 800 G the polarized bath dephases faster than P1. The field dependence of every bath, P1 included, follows the mean moment of its centres along the field. For the Hahn echo, exchange with on-axis bath centres and bath relaxation (T1 = 6 ms) limit the gain to 1.2 times the P1 value at 25 G. Optical polarization of an NV- bath at low field therefore offers dephasing times beyond the P1 limit of nitrogen-rich diamond.
Related
- Theoretical study of nitrogen-vacancy spin coherence enhanced by vacancy aggregation in diamond using cluster-correlation expansion
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- Experimental Benchmarking of a 256-Qubit Room-Temperature NV-Diamond Quantum Processor with an Optically Programmable Biomolecular Quantum Bus
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BibTeX
@misc{shinei2026lowfield,
title = {{Low-field dephasing time of an optically polarized NV$^-$ spin bath beyond the P1 limit in diamond: a cluster-correlation-expansion and exact spin-bath study}},
author = {Chikara Shinei},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.29279},
eprint = {2610.29279},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.29279},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Low-field dephasing time of an optically polarized NV^- spin bath beyond the P1 limit in diamond: a cluster-correlation-expansion and exact spin-bath study
AU - Chikara Shinei
PY - 2026
DA - 2026/10/21
PB - arXiv
DO - 10.48550/arxiv.2610.29279
UR - https://arxiv.org/abs/2610.29279
AB - Dense ensembles of nitrogen-vacancy (NV^-) centres in nitrogen-rich diamond dephase on the electron spins of the substitutional nitrogen (P1) centres. If the paramagnetic nitrogen is instead converted into NV^- centres, the laser that initializes the sensor also pumps the bath into m_s = 0, a state with no moment along its own axis. Using cluster-correlation-expansion (CCE) calculations, combined with an exact solver for probe-bath exchange and with no adjustable parameter, this paper asks whether such an optically polarized NV^- bath dephases a sensor more slowly than a P1 bath of the same density. The answer is set by the field. In a field along [111], three quarters of the bath centres lie off the field axis, and the moment of their m_s = 0 state along the field grows from 0.04 at 25 G to 0.46 at 300 G and 0.81 at 800 G. At 25 G the polarized bath is therefore nearly silent: at 10^17 cm^−3 the dephasing time T_2^* of a separately addressed ^15NV^- probe is 112 us, six times the 18.1 us of a P1 bath, and still 2.4 times at 90 % polarization; an ensemble measurement gains a factor of two. At 300 G the advantage over P1 shrinks to 1.4, and at 800 G the polarized bath dephases faster than P1. The field dependence of every bath, P1 included, follows the mean moment of its centres along the field. For the Hahn echo, exchange with on-axis bath centres and bath relaxation (T_1 = 6 ms) limit the gain to 1.2 times the P1 value at 25 G. Optical polarization of an NV^- bath at low field therefore offers dephasing times beyond the P1 limit of nitrogen-rich diamond.
ER -