We report successful introduction of negatively charged nitrogen-vacancy (NV(-)) centers in a 5 nm thin, isotopically enriched ([(12)C] = 99.99%) diamond layer by CVD. The present method allows for the formation of NV(-) in such a thin layer even when the surface is terminated by hydrogen atoms. NV(-) centers are found to have spin coherence times of between T2 ~ 10-100 μs at room temperature. Changing the surface termination to oxygen or fluorine leads to a slight increase in the NV(-) density, but not to any significant change in T2. The minimum detectable magnetic field estimated by this T2 is 3 nT after 100 s of averaging, which would be sufficient for the detection of nuclear magnetic fields exerted by a single proton. We demonstrate the suitability for nanoscale NMR by measuring the fluctuating field from ~10(4) proton nuclei placed on top of the 5 nm diamond film.

We report on a microwave planar ring antenna specifically designed for optically-detected magnetic resonance (ODMR) of nitrogen-vacancy (NV) centers in diamond. It has the resonance frequency at around 2.87 GHz with the bandwidth of 400 MHz, ensuring that ODMR can be observed under external magnetic fields up to 100 G without the need of adjustment of the resonance frequency. It is also spatially uniform within the 1-mm-diameter center hole, enabling the magnetic-field imaging in the wide spatial range. These features facilitate the experiments on quantum sensing and imaging using NV centers at room temperature.

We have investigated photoinduced spectral changes of excitons in inorganic-organic layered semiconductors, ͑C 6 H 5 C 2 H 4 NH 3 ͒ 2 PbI 4 ͑PhE-PbI 4 ͒ and ͑C 6 H 13 NH 3 ͒ 2 PbI 4 ͑C6-PbI 4 ͒, by means of the subpicosecond pump-probe spectroscopy. The two semiconductors consist of the same inorganic layers and different organic layers. In the two substances, the blueshift and the bleaching of the exciton are observed. It is found that both of the blueshift and the bleaching are considerably stronger in C6-PbI 4 than in PhE-PbI 4 . The weight of the blueshift relative to the bleaching is larger in PhE-PbI 4 than in C6-PbI 4 . These differences are qualitatively explained in terms of the stronger dielectric confinement in C6-PbI 4 than in PhE-PbI 4 due to the lower dielectric constant of the organic layers in C6-PbI 4 than in PhE-PbI 4 . Delay time dependences of the blueshift and the bleaching and their polarization dependences are understood as being due to the exciton relaxation in the angular momentum space with rates of 2.7 and 4.1 ps −1 for PhE-PbI 4 and C6-PbI 4 , respectively.

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We investigated the photoluminescence of individual air-suspended single-walled carbon nanotubes (SWNTs) from 6 to 300 K. Time-resolved and antibunching measurements over the telecommunication wavelength range were performed using a superconducting single-photon detector. We detected moderate temperature independent antibunching behavior over the whole temperature range studied. To investigate the exciton dynamics, which is responsible for the antibunching behavior, we measured excitation-power and temperature dependence of the photoluminescence spectra and lifetime decay curves. These measurements suggested an exciton confinement effect that is likely caused by high-dielectric amorphous carbon surrounding the SWNTs. These results indicate that SWNTs are good candidates for light sources in quantum communication technologies operating in the telecommunication wavelength range and at room temperature.

Nitrogen-vacancy (NV) centers in diamond are considered sensors for detecting magnetic fields. Pulsed optically detected magnetic resonance (ODMR) is typically used to detect AC magnetic fields; however, this technique can only be implemented after careful calibration that involves aligning an external static magnetic field, measuring continuous-wave (CW) ODMR, determining the Rabi frequency, and setting the microwave phase. In contrast, CW-ODMR can be simply implemented by continuous application of green CW laser and a microwave filed. In this letter, we report a method that uses NV centers and CW-ODMR to detect AC magnetic fields. Unlike conventional methods that use NV centers to detect AC magnetic fields, the proposed method requires neither a pulse sequence nor an externally applied DC magnetic field; this greatly simplifies the procedure and apparatus needed to implement this method. This method provides a sensitivity of 2.5 µT/ Hz at room temperature. Thus, this simple alternative to existing AC magnetic field sensors paves the way for a practical and feasible quantum sensor.

An ensemble of nitrogen-vacancy (NV) centers in diamond is an attractive device to detect small magnetic fields. In particular, by exploiting the fact that the NV center can be aligned along one of four different axes due to C3ν symmetry, it is possible to extract information concerning vector magnetic fields. However, in the conventional scheme, low readout contrasts of the NV centers significantly decrease the sensitivity of the vector magnetic field sensing. Here, we propose a way to improve the sensitivity of the vector magnetic field sensing of the NV centers using multi-frequency control. Since the Zeeman energy of the NV centers depends on the direction of the axis, we can independently control the four types of NV centers using microwave pulses with different frequencies. This allows us to use every NV center for the vector field detection in parallel, which effectively increases the readout contrast. Our results pave the way to realize a practical diamond-based vector field sensor.The detection of small magnetic fields is important in the field of metrology, because there are many potential applications in biology and medical science. The performance of a magnetic field sensor is characterized by its spatial resolution and sensitivity; therefore, a significant amount of effort has been devoted to creating a device that can measure small magnetic fields in a local region [1][2][3].Nitrogen vacancy (NV) centers in diamond are fascinating candidates with which to construct a magnetic field sensor [4][5][6][7]. The NV center is a spin 1 system, and the frequency of the | ± 1 states can be shifted by magnetic fields. We can use this system as an effective two-level system spanned by |0 and |1 with a frequency selectivity where | − 1 is significantly detuned. We can implement gate operations of the spins in NV centers using microwave pulses [8][9][10][11]. It is possible to detect DC (AC) magnetic fields by implementing a Ramsey interference (spin echo) measurement [4][5][6]. Moreover, NV centers have a long coherence time, e.g., a few milli-seconds at a room temperature and a second at low temperature [12][13][14]. In addition, because the NV centers can be strongly coupled with optical photons, we can read out the state of the NV centers via fluorescence from the optical transitions [9,10]. The NV centers can be embedded in nanocrystals, which allows the NV centers to interact with local magnetic fields [15]. These properties are prerequisite to realizing a high-performance sensor for magnetic fields.Recently, vector magnetic field sensing by NV centers has become an active area of interest [16][17][18][19][20][21]. The NV center is aligned along one of four different axes due to C 3ν symmetry. The Zeeman energies of the NV centers are determined by gµ b B · d j (j = 1, 2, 3, 4) where g denotes the g factor, µ b denotes a Bohr magneton, B denotes the magnetic fields, and d j denotes the direction of the j-th NV axis. By sequentially performing Ramsey interference or spin echo measurements on NV centers with...

An ensemble of nitrogen-vacancy (NV) centers in diamond is a fascinating candidate to realize a sensitive magnetic field sensor. In particular, since the axes of the NV centers are distributed along four directions, a collection of measurement data from NV centers with different axes provides information on the vector components of a magnetic field. However, in the conventional approach, the low measurement contrast of NV centers limits the sensitivity of vector magnetic field sensing. Recently, to overcome this problem, multi-frequency control of the NV centers has been proposed. The key idea is that the four types of NV centers with different axes are simultaneously controlled by multi-frequency microwave pulses. Here, we demonstrate vector magnetic field sensing with an ensemble of NV centers in diamond via such multi-frequency control with pulsed-type measurements. We use Hahn echo pulses and extract information on the vector components of an applied AC magnetic field. We find that the sensitivity of diamond-based vector field sensing with multi-frequency control is better than that with single-frequency control for every vector component of a magnetic field.Magnetic field sensors have significant applications in chemistry, biology, and medical science. For example, in electron spin resonance, which is a widely used technique in chemistry, magnetic field sensors play an important role in obtaining information about the electron spin. Magnetoencephalography is a clinical technique for measuring electrical activity in the brain via magnetic field sensing, thereby providing information about brain function. Magnetic resonance imaging allows examination of the internal structure of the human body based on magnetic field information. For the magnetic field sensors used in these contexts, sensitivity and spatial resolution are essential parameters to quantify performance, and much effort has been devoted to measuring weak magnetic fields in local regions. 1-3