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Quantum magnetic sensors based on nitrogen vacancy (NV) centers are expected to be used for various biological and medical applications. Continuously excited (CE) Ramsey magnetometry is one of the most sensitive measurement protocols and has the potential to improve the sensitivity of sensors using additional quantum manipulations to extend the spin dephasing time. In a typical ensemble NV measurement, the spin dephasing time is limited by inhomogeneous coupling. To overcome this limitation, a magnetometry that extends the CE Ramsey protocol with a double‐quantum (DQ) Ramsey sequence and spin bath driving is developed. It is demonstrated that the electric noise due to the spatial inhomogeneity of the crystal strain is cancelled out by the DQ Ramsey, and the magnetic noise due to the P1 centers was suppressed by spin bath driving. Compared to the conventional CE Ramsey, the CE‐DQ Ramsey with spin bath driving effectively doubles the gyromagnetic ratio and yields a twofold extension of T2*, corresponding to a fourfold enhancement of the photon‐shot‐noise limited sensitivity. [ABSTRACT FROM AUTHOR]

To demonstrate the application capability of the diamond quantum sensor as an electric vehicle (EV) battery monitor, we (i) investigated the measurable current in a real car noise level and (ii) compared the linearity with conventional sensors. Consequently, (i) we could measure a 20 mA current pulse even under an external magnetic field of 80 µT, which is larger than that of 50 µT around the EV battery module in a real car during driving. The 20 mA pulse measurement corresponds to the EV battery state of charge estimation accuracy of 0.2% in the standard driving pattern, which is smaller than the present level of 10%. (ii) The linearity degradation seen in the Hall sensor near the upper limit of the measurement range was not seen in the diamond sensor. Although the Hall sensor and the shunt resistor showed linearity degradation in the current range of several tens of amperes or less, the degradation was smaller for the diamond sensor. The transverse magnetic field effect in the diamond sensor on the linearity was estimated to be less than 0.01% for a several-degree misalignment of the sensor surface to the magnetic field direction and under a 340 A current. This article is part of the Theo Murphy meeting issue 'Diamond for quantum applications'. [ABSTRACT FROM AUTHOR]

Extending the spin‐dephasing time (T2*) of perfectly aligned nitrogen‐vacancy (NV) centers in large‐volume chemical vapor deposition (CVD) diamonds leads to enhanced DC magnetic sensitivity. However, T2* of the NV centers is significantly reduced by the stress distribution in the diamond film as its thickness increases. To overcome this issue, they developed a method to mitigate the stress distribution in the CVD diamond films, leading to a T2* extension of the ensemble NV centers. CVD diamond films of ≈60 µm thickness with perfectly aligned NV centers are formed on (111) diamond substrates with misorientation angles of 2.0°, 3.7°, 5.0°, and 10.0°. The study found that T2* of the ensemble of NV centers increased to approach its value limited only by the electron and nuclear spin bath with increasing the misorientation angle. Microscopic stress imaging revealed that the stress distribution is highly inhomogeneous along the depth direction in the CVD diamond film at low misorientation angles, whereas the inhomogeneity is largely suppressed on highly misoriented substrates. The reduced stress distribution possibly originates from the reduction of the dislocation density in the CVD diamond. This study provides an important method for synthesizing high‐quality diamond materials for use in highly sensitive quantum sensors. [ABSTRACT FROM AUTHOR]

Scanning tunneling microscopy and spectroscopy are used to study the initial stage of the molecular beam epitaxy of Si and Ge on Si(111) - 7 * 7 substrates with atomically straight steps. The results have shown localized electronic states on the Ge nanoclusters.

Extending the spin dephasing time (T2*) of perfectly aligned nitrogen‐vacancy (NV) centers in large‐volume chemical vapor deposition (CVD) diamond leads to enhanced magnetic sensitivity. In article number 2300194, Mutsuko Hatano and co‐workers develop a method to reduce the stress distribution in CVD diamond layers and succeed in extending T2* of ensemble NV centers..By Takeyuki Tsuji; Takeharu Sekiguchi; Takayuki Iwasaki and Mutsuko HatanoReported by Author; Author; Author; Author [Extracted from the article]

Pulsed electron paramagnetic resonance spectroscopy of the photoexcited, metastable triplet state of the oxygen-vacancy center in silicon reveals that the lifetime of the ms = ± 1 véis differs significantly from that of the ms = 0 state. We exploit this significant difference in decay rates to the ground singlet state to achieve nearly ∼100% electron-spin polarization within the triplet. We further demonstrate the transfer of a coherent state of the triplet electron spin to, and from, a hyperfine-coupled, nearest-neighbor 29 Si nuclear spin. We measure the coherence time of the 29Si nuclear spin employed in this operation and find it to be unaffected by the presence of the triplet electron spin and equal to the bulk value measured by nuclear magnetic resonance. [ABSTRACT FROM AUTHOR]

To demonstrate the application capability of the diamond quantum sensor as an electric vehicle (EV) battery monitor, we (i) investigated the measurable current in a real car noise level and (ii) compared the linearity with conventional sensors. Consequently, (i) we could measure a 20 mA current pulse even under an external magnetic field of 80 µT, which is larger than that of 50 µT around the EV battery module in a real car during driving. The 20 mA pulse measurement corresponds to the EV battery state of charge estimation accuracy of 0.2% in the standard driving pattern, which is smaller than the present level of 10%. (ii) The linearity degradation seen in the Hall sensor near the upper limit of the measurement range was not seen in the diamond sensor. Although the Hall sensor and the shunt resistor showed linearity degradation in the current range of several tens of amperes or less, the degradation was smaller for the diamond sensor. The transverse magnetic field effect in the diamond sensor on the linearity was estimated to be less than 0.01% for a several-degree misalignment of the sensor surface to the magnetic field direction and under a 340 A current. This article is part of the Theo Murphy meeting issue 'Diamond for quantum applications'.

Pulsed electron paramagnetic resonance spectroscopy of the photoexcited, metastable triplet state of the oxygen-vacancy center in silicon reveals that the lifetime of the m(s)=±1 sublevels differs significantly from that of the m(s)=0 state. We exploit this significant difference in decay rates to the ground singlet state to achieve nearly ~100% electron-spin polarization within the triplet. We further demonstrate the transfer of a coherent state of the triplet electron spin to, and from, a hyperfine-coupled, nearest-neighbor (29)Si nuclear spin. We measure the coherence time of the (29)Si nuclear spin employed in this operation and find it to be unaffected by the presence of the triplet electron spin and equal to the bulk value measured by nuclear magnetic resonance.