Diamond quantum magnetometer with dc sensitivity of sub-10 pT <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><mml:mi>Hz</mml:mi><mml:msup><mml:mspace width="0.2em"/><mml:mrow><mml:mo>−</mml:mo><mml:mn>1</mml:mn><mml:mo>/</mml:mo><mml:mn>2</mml:mn></mml:mrow></mml:msup></mml:math> toward measurement of biomagnetic field
Naota Sekiguchi, Motofumi Fushimi, Akihiko Yoshimura, Chikara Shinei, Masashi Miyakawa, Takashi Taniguchi, Tokuyuki Teraji, Hiroshi Abe, Shinobu Onoda, Takeshi Ohshima, Masaharu Hatano, Masaki Sekino, Takayuki Iwasaki
Abstract
We present a sensitive diamond quantum sensor with a magnetic field sensitivity of $9.4\ifmmode\pm\else\textpm\fi{}0.1\phantom{\rule{0.2em}{0ex}}\mathrm{pT}/\sqrt{\mathrm{Hz}}$ in a near-dc frequency range of 5 to 100 Hz. This sensor is based on the continuous-wave optically detected magnetic resonance of an ensemble of nitrogen-vacancy centers along the [111] direction in a diamond (111) single crystal. The long ${T}_{2}^{\ensuremath{\ast}}\ensuremath{\sim}2\phantom{\rule{0.2em}{0ex}}\text{\ensuremath{\mu}}\mathrm{s}$ in our diamond and the reduced intensity noise in laser-induced fluorescence result in remarkable sensitivity among diamond quantum sensors. Based on an Allan-deviation analysis, we demonstrate that a subpicotesla field of 0.3 pT is detectable by interrogating the magnetic field for a few thousand seconds. The sensor head is compatible with various practical applications and allows a minimum measurement distance of about 1 mm from the sensing region. The proposed sensor facilitates the practical application of diamond quantum sensors. The sensitivity presented is realized without a magnetic flux concentrator, so that a sensitivity of tens of $\mathrm{fT}/\sqrt{\mathrm{Hz}}$ can be achievable by using a flux concentrator.