CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application is related to U.S. Patent Application No. 15/468,397 filed March 24, 2017, entitled "HIGH SPEED SEQUENTIAL CANCELLATION FOR PULSED MODE", the content of which is incorporated herein by reference in its entirety.

FIELD

[0002] The subject technology generally relates without limitation to magnetometers, and for example, to a high speed sequential cancellation for pulsed mode.

BACKGROUND

[0003] A number of industrial applications, as well as scientific areas such as physics and chemistry can benefit from magnetic detection and imaging with a device that has extraordinary sensitivity, ability to capture signals that fluctuate very rapidly (bandwidth) all with a substantive package that is extraordinarily small in size and efficient in power. Many advanced magnetic imaging systems can operate in restricted conditions, for example, high vacuum and/or cryogenic temperatures, which can make them inapplicable for imaging applications that require ambient or other conditions. Furthermore, small size, weight and power (SWAP) magnetic sensors of moderate sensitivity, vector accuracy, and bandwidth are valuable in many applications.

SUMMARY

[0004] Some embodiments provide methods and systems for high bandwidth acquisition of magnetometer data with increased sensitivity. In some implementations, a reference signal may be utilized prior to acquisition of a measured signal for a magnetometer. This reference signal may provide a full repolarization of a magneto-optical defect center material prior to acquiring the reference signal. The reference signal may then be used to adjust the measured signal to correct for potential fluctuations in optical excitation power levels, which can cause a

proportional fluctuation in the measured signal. However, such a full repolarization and added reference signal before each measured signal may reduce the bandwidth of the magnetometer and may also increase measurement noise, and therefore decrease sensitivity, by including noise from the reference signal when calculating the resulting processed signal. To increase bandwidth and sensitivity, the reference signal may be omitted such that only a radiofrequency (RF) pulse excitation sequence is included between measurements. In some implementations, a fixed "system rail" photo measurement may be obtained initially and used as a fixed reference signal for subsequent measured signals. The fixed, nominal reference signal can substantially compensate for intensity shifts for the magnetometer without decreasing bandwidth or sensitivity. In other implementations, additional signal processing may be utilized to adjust for drift, jitter, or other variations in intensity levels.

[0005] Some embodiments may include a magnetometer and a controller. The magnetometer may include a magneto-optical defect center material, an optical excitation source, a

radiofrequency (RF) excitation source, and an optical sensor. The controller may be configured to activate a radiofrequency (RF) pulse sequence for the RF excitation source to apply a RF field to the magneto-optical defect center material, acquire a nominal ground reference signal for the magneto-optical defect center material, and acquire a magnetic field measurement from the magneto-optical defect center material using the optical sensor. The magnetic field measurement may be acquired independent of a reference magnetic field measurement.

[0006] In some implementations, acquiring the repetitive magnetic field measurement can include a polarization pulse length. In some implementations, the controller may processes the repetitive magnetic field measurement directly to obtain magnetometry measurements. In some implementations, the controller may further be configured to determine a vector of the repetitive magnetic field measurement. In some implementations, the controller may use a fixed system rail photo measurement as a nominal reference value. The magneto-optical defect center material may be a diamond having nitrogen vacancies. The controller may be further configured to process the magnetic field measurement.

[0007] Other implementations may relate to a method for operating a magnetometer having a magneto-optical defect center material. The method may include activating a radiofrequency (RF) pulse sequence to apply an RF field to the magneto-optical defect center material, acquiring a nominal ground reference signal for the magneto-optical defect center material, and acquiring a magnetic field measurement using the magneto-optical defect center material. The magnetic field measurement may be acquired independent of a reference magnetic field measurement.

[0008] In some implementations, acquiring the magnetic field measurement can include a polarization pulse length. In some implementations, acquiring a magnetic field measurement may include processing the magnetic field measurement directly to obtain magnetometry measurements. In some implementations, the method may further include determining a vector of the repetitive magnetic field measurement. In some implementations, acquiring a magnetic field measurement may include using a fixed system rail photo measurement as a nominal reference value. The magneto-optical defect center material may be a diamond having nitrogen vacancies. The method can further include processing the magnetic field measurement using a controller.

[0009] Yet other implementations relate to a sensor that may include a magneto-optical defect center material, a radiofrequency (RF) excitation source, and a controller. The controller may be configured to activate a radiofrequency (RF) pulse sequence for the RF excitation source to apply a RF field to the magneto-optical defect center material, acquire a nominal ground reference signal for the magneto-optical defect center material, and acquire a magnetic field measurement from the magneto-optical defect center material. The magnetic field measurement may be acquired independent of a reference magnetic field measurement.

[0010] In some implementations, acquiring the magnetic field measurement can include a polarization pulse length. In some implementations, the controller may processes the magnetic field measurement directly to obtain magnetometry measurements. In some implementations, the controller may further be configured to determine a vector of the magnetic field measurement. In some implementations, the controller may use a fixed system rail photo measurement as a nominal reference value. The magneto-optical defect center material may be a diamond having nitrogen vacancies. The controller may be further configured to process the magnetic field measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the disclosure will become apparent from the description, the drawings, and the claims, in which:

[0012] FIG. 1 illustrates an orientation of an NV center in a diamond lattice;

[0013] FIG. 2 illustrates an energy level diagram showing energy levels of spin states for the

NV center;

[0014] FIG. 3 illustrates a schematic diagram of a NV center magnetic sensor system;

[0015] FIG. 4 is a graph illustrating the fluorescence as a function of an applied RF frequency of an NV center along a given direction for a zero magnetic field, and also for a non-zero magnetic field having a component along the NV axis;

[0016] FIG. 5 is a graph illustrating the fluorescence as a function of an applied RF frequency for four different NV center orientations for a non-zero magnetic field;

[0017] FIG. 6 is a graphical diagram depicting a Ramsey pulse sequence;

[0018] FIG. 7 is a graphical diagram of a magnetometer system using a reference signal acquisition prior to RF pulse excitation sequence and measured signal acquisition;

[0019] FIG. 8 is a graphical diagram of a magnetometer system omitting the reference signal acquisition of FIG. 6 prior to RF pulse excitation sequence and measured signal acquisition;

[0020] FIG. 9 is a graphical diagram depicting a reference signal intensity relative to detune frequency and a measured signal intensity relative to detune frequency;

[0021] FIG. 10 is a graphical diagram depicting a slope relative to laser pulse width for a system implementing a reference signal and a system omitting the reference signal;

[0022] FIG. 11 is a graphical diagram depicting a sensitivity relative to polarization pulse length for a system implementing a reference signal and a system omitting the reference signal;

[0023] FIG. 12 is a process diagram for operating a magnetometer without using a reference signal; and

[0024] FIG. 13 is a block diagram depicting a general architecture for a computer system that may be employed to implement various elements of the systems and methods described and illustrated herein. [0025] It will be recognized that some or all of the figures are schematic representations for purposes of illustration. The figures are provided for the purpose of illustrating one or more embodiments with the explicit understanding that they will not be used to limit the scope or the meaning of the claims.

DETAILED DESCRIPTION

[0026] Following below are more detailed descriptions of various concepts related to, and implementations of, methods, apparatuses, and systems for high bandwidth acquisition of magnetometer data with increased sensitivity. Some embodiments increase bandwidth and sensitivity of the magnetometer by eliminating the need for a reference signal that requires full repolarization of the magneto-optical defect center material prior to acquisition. Eliminating the reference signal eliminates the time needed to repolarize the magneto-optical defect center material and the acquisition time for the reference signal. An optional ground reference, a fixed "system rail" photo measurement, and/or additional signal processing may be utilized to adjust for variations in intensity levels.

[0027] Atomic-sized magneto-optical defect centers, such as nitrogen-vacancy (NV) centers in diamond lattices, have excellent sensitivity for magnetic field measurement and enable fabrication of small magnetic sensors. Magneto-optical defect center materials include but are not be limited to diamonds, Silicon Carbide (SiC), Phosphorous, and other materials with nitrogen, boron, carbon, silicon, or other defect centers. The diamond nitrogen vacancy (DNV) sensors are maintained in room temperature and atmospheric pressure and can be even used in liquid environments. A green optical source (e.g., a micro-LED) can optically excite NV centers of the DNV sensor and cause emission of fluorescence radiation (e.g., red light) under off- resonant optical excitation. A magnetic field generated, for example, by a microwave coil can probe triplet spin states (e.g., with ms = -1, 0, +1) of the NV centers to split in relation to an external magnetic field projected along the NV axis, resulting in two spin resonance frequencies. The difference between the two spin resonance frequencies can correlate to a measure of the strength of the external magnetic field. A photo detector can measure the fluorescence (red light) emitted by the optically excited NV centers. Nitrogen-vacancy centers (NV centers) are defects in a diamond's crystal structure, which can purposefully be manufactured in synthetic diamonds as shown in Figure 1. In general, when excited by green light and microwave radiation, the NV centers cause the diamond to generate red light. When excited with green light, the NV defect centers generate red light fluorescence. After sufficient time (on order of nanoseconds to microseconds) the fluorescence counts stabilize. When microwave radiation is added, the NV electron spin states are changed, and this results in a change in intensity of the red fluorescence. The changes in fluorescence may be recorded as a measure of electron spin resonance. . By measuring the changes, the NV centers may be used to accurately detect the magnetic field strength.

[0028] The NV center may exist in a neutral charge state or a negative charge state.

Conventionally, the neutral charge state uses the nomenclature NV°, while the negative charge state uses the nomenclature NV, which is adopted in this description.

[0029] The NV center may have a number of electrons, including three unpaired electrons, each one from the vacancy to a respective of the three carbon atoms adjacent to the vacancy, and a pair of electrons between the nitrogen and the vacancy. The NV center, which is in the negatively charged state, also includes an extra electron.

[0030] The NV center has rotational symmetry and, as shown in FIG. 2, has a ground state, which is a spin triplet with ³ A ₂ symmetry with one spin state m _s = 0, and two further spin states m _s = +1 , and m _s = - 1. In the absence of an external magnetic field, the m _s = ±1 energy levels are offset from the m _s = 0 due to spin-spin interactions, and the m _s = ±1 energy levels are degenerate, i.e., they have the same energy. The m _s = 0 spin state energy level is split from the m _s = ±1 energy levels by an energy of approximately 2.87 GHz for a zero external magnetic field.

[0031] Introducing an external magnetic field with a component along the NV axis lifts the degeneracy of the m _s = ± 1 energy levels, splitting the energy levels m _s = ± 1 by an amount 2gμBB _z , where g is the Lande g-factor, μ _Β is the Bohr magneton, and B _z is the component of the external magnetic field along the NV axis. This relationship is correct to a first order and inclusion of higher order corrections is a straightforward matter. [0032] The NV center electronic structure further includes an excited triplet state E with corresponding m _s = 0 and m _s = ±1 spin states. The optical transitions between the ground state ³ A ₂ and the excited triplet ³ E are predominantly spin conserving, meaning that the optical transitions are between initial and final states that have the same spin. For a direct transition between the excited triplet ³ E and the ground state ³ A ₂ , a photon of red light is emitted with a photon energy corresponding to the energy difference between the energy levels of the transitions.

[0033] There is, however, an alternative non-radiative decay route from the triplet ³ E to the ground state ³ A ₂ via intermediate electron states, which are thought to be intermediate singlet states A, E with intermediate energy levels. Significantly, the transition rate from the m _s = ±1 spin states of the excited triplet ³ E to the intermediate energy levels is significantly greater than the transition rate from the m _s = 0 spin state of the excited triplet ³ E to the intermediate energy levels. The transition from the singlet states A, E to the ground state triplet ³ A ₂ predominantly decays to the m _s = 0 spin state over the m _s = ±1 spins states. These features of the decay from the excited triplet ³ E state via the intermediate singlet states A, E to the ground state triplet ³ A ₂ allows that if optical excitation is provided to the system, the optical excitation will eventually pump the NV center into the m _s = 0 spin state of the ground state ³ A ₂ . In this way, the population of the m _s = 0 spin state of the ground state ³ A ₂ may be "reset" to a maximum polarization determined by the decay rates from the triplet ³ E to the intermediate singlet states.

[0034] Another feature of the decay is that the fluorescence intensity due to optically stimulating the excited triplet ³ E state is less for the m _s = ±1 states than for the m _s = 0 spin state. This is so because the decay via the intermediate states does not result in a photon emitted in the fluorescence band, and because of the greater probability that the m _s = ±1 states of the excited triplet ³ E state will decay via the non-radiative decay path. The lower fluorescence intensity for the m _s = ±1 states than for the m _s = 0 spin state allows the fluorescence intensity to be used to determine the spin state. As the population of the m _s = ±1 states increases relative to the m _s = 0 spin, the overall fluorescence intensity will be reduced.

[0035] FIG. 3 is a schematic diagram illustrating a NV center magnetic sensor system 300 that uses fluorescence intensity to distinguish the m _s = ±1 states, and to measure the magnetic field based on the energy difference between the m _s = +1 state and the m _s = -1 state, as manifested by the RF frequencies corresponding to each state. The system 300 includes an optical excitation source 310, which directs optical excitation to an NV diamond material 320 with NV centers. The system further includes an RF excitation source 330, which provides RF radiation to the NV diamond material 320. Light from the NV diamond may be directed through an optical filter 350 to an optical detector 340.

[0036] The RF excitation source 330 may be a microwave coil, for example. The RF excitation source 330, when emitting RF radiation with a photon energy resonant with the transition energy between ground m _s = 0 spin state and the m _s = +1 spin state, excites a transition between those spin states. For such a resonance, the spin state cycles between ground m _s = 0 spin state and the m _s = +1 spin state, reducing the population in the m _s = 0 spin state and reducing the overall fluorescence at resonances. Similarly, resonance and a subsequent decrease in fluorescence intensity occurs between the m _s = 0 spin state and the m _s = -1 spin state of the ground state when the photon energy of the RF radiation emitted by the RF excitation source is the difference in energies of the m _s = 0 spin state and the m _s = -1 spin state.

[0037] The optical excitation source 310 may be a laser or a light emitting diode, for example, which emits light in the green (light having a wavelength such that the color is green), for example. The optical excitation source 310 induces fluorescence in the red, which corresponds to an electronic transition from the excited state to the ground state. Light from the NV diamond material 320 is directed through the optical filter 350 to filter out light in the excitation band (in the green, for example), and to pass light in the red fluorescence band, which in turn is detected by the detector 340. The optical excitation light source 310, in addition to exciting fluorescence in the diamond material 320, also serves to reset the population of the m _s = 0 spin state of the ground state ³ A ₂ to a maximum polarization, or other desired polarization.

[0038] For continuous wave excitation, the optical excitation source 310 continuously pumps the NV centers, and the RF excitation source 330 sweeps across a frequency range that includes the zero splitting (when the m _s = ±1 spin states have the same energy) photon energy of approximately 2.87 GHz. The fluorescence for an RF sweep corresponding to a diamond material 320 with NV centers aligned along a single direction is shown in FIG. 4 for different magnetic field components B _z along the NV axis, where the energy splitting between the m _s = -1 spin state and the m _s = +1 spin state increases with B _z . Thus, the component B _z may be determined. Optical excitation schemes other than continuous wave excitation are contemplated, such as excitation schemes involving pulsed optical excitation, and pulsed RF excitation.

Examples of pulsed excitation schemes include Ramsey pulse sequence (described in more detail below), spin echo pulse sequence, etc.

[0039] In general, the diamond material 320 will have NV centers aligned along directions of four different orientation classes. FIG. 5 illustrates fluorescence as a function of RF frequency for the case where the diamond material 320 has NV centers aligned along directions of four different orientation classes. In this case, the component B _z along each of the different orientations may be determined. These results, along with the known orientation of

crystallographic planes of a diamond lattice, allow not only the magnitude of the external magnetic field to be determined, but also the direction of the magnetic field.

[0040] While FIG. 3 illustrates an NV center magnetic sensor system 300 with NV diamond material 320 with a plurality of NV centers, in general, the magnetic sensor system may instead employ a different magneto-optical defect center material, with a plurality of magneto-optical defect centers. Magneto-optical defect center materials include but are not be limited to diamonds, Silicon Carbide (SiC), Phosphorous, and other materials with nitrogen, boron, carbon, silicon, or other defect centers. The electronic spin state energies of the magneto-optical defect centers shift with magnetic field, and the optical response, such as fluorescence, for the different spin states is not the same for all of the different spin states. In this way, the magnetic field may be determined based on optical excitation, and possibly RF excitation, in a corresponding way to that described above with NV diamond material.

[0041] A Ramsey pulse sequence is a pulsed RF laser scheme that is believed to measure the free precession of the magnetic moment in the diamond material 320 with NV centers, and is a technique that quantum mechanically prepares and samples the electron spin state. FIG. 6 is an example of a schematic diagram illustrating the Ramsey pulse sequence. As shown in FIG. 6, a Ramsey pulse sequence includes optical excitation pulses and RF excitation pulses over a five- step period. In a first step, during a period 0, a first optical excitation pulse 610 is applied to the system to optically pump electrons into the ground state (i.e., m _s = 0 spin state). This is followed by a first RF excitation pulse 620 (in the form of, for example, a microwave (MW) π/2 pulse) during a period 1. The first RF excitation pulse 620 sets the system into superposition of the m _s = 0 and m _s = +1 spin states (or, alternatively, the m _s = 0 and m _s = -1 spin states, depending on the choice of resonance location). During a period 2, the system is allowed to freely precess (and dephase) over a time period referred to as tau (τ). During this free precession time period, the system measures the local magnetic field and serves as a coherent integration. Next, a second RF excitation pulse 630 (in the form of, for example, a MW π/2 pulse) is applied during a period 3 to project the system back to the m _s = 0 and m _s = +1 basis. Finally, during a period 4, a second optical pulse 640 is applied to optically sample the system and a measurement basis is obtained by detecting the fluorescence intensity of the system. The RF excitation pulses applied are provided at a given RF frequency in relation to the Lorentzians such as referenced in connection with FIG. 5.

[0042] FIG. 7 depicts a graph 700 of a magnetometer system using a reference signal 710 acquisition prior to RF pulse excitation sequence 720 and measured signal 730 acquisition. A contrast measurement between the measured signal 730 and the reference signal 710 for a given pulsed sequence is then computed as a difference between a processed read-out fluorescence level from the measured signal acquisition 730 and a processed reference fluorescence measurement from the reference signal 710. The processing of the measured signal 730 and/or the reference signal 710 may involve computation of the mean fluorescence over each of the given intervals. The reference signal 710 is to compensate for potential fluctuations in the optical excitation power level, which can cause a proportional fluctuation in the measurement and readout fluorescence measurements. Thus, in some implementations the magnetometer includes a full repolarization between measurements with a reference fluorescence intensity (e.g., the reference signal 710) captured prior to RF excitation (e.g., RF pulse excitation sequence 720) and the subsequent magnetic b field measurement data 730. This approach may reduce sensor bandwidth and increase measurement noise by requiring two intensity estimates per magnetic b field measurement. For a DNV magnetometer, this means that it needs full repolarization of the ensemble diamond [NV] states between measurements. In some instances, the bandwidth considerations provide a high laser power density trade space in sensor design, which can impact available integration time and achievable sensitivity.

[0043] FIG. 8 depicts a graph 800 of a magnetometer system omitting a reference signal acquisition prior to RF pulse excitation sequence 820 and measured signal 830 acquisition. The RF pulse excitation sequence 820 may correspond to periods 1-3 of Figure 6 and the measured signal acquisition 830 may correspond to period 4 of Figure 6. The graph 800 depicts the amplitude of optical light emitted from a magneto-optical defect center material as measured by an optical detector 340, such as a photodiode, over time. The system processes the post RF sequence read-out measurement from the measured signal 830 directly to obtain magnetometry measurements. The processing of the measured signal 830 may involve computation of the mean fluorescence over each of the given intervals. In some implementations, a fixed "system rail" photo measurement is obtained and used as a nominal reference to compensate for any overall system shifts in intensity offset. In some implementations, an optional ground reference signal 810 may be obtained during the RF pulse excitation sequence 820, such as during period 2 of Figure 6, to be used as an offset reference. Some embodiments provide faster acquisition times, reduced or eliminated noise from the reference signal, and increased potential detune intensity peak to peak contrast.

[0044] Figure 9 is a graphical diagram of an intensity of a measured signal 910 from an optical detector 340 relative to an intensity of a reference signal 920 from the optical detector 340 over a range of detune frequencies. When using a reference signal 920, the reference signal 920 will contain signal information from a prior RF pulse for a finite period of time. This prior signal information in the reference signal 920 reduces available detune peak to peak intensity range and slope for a detune point for positive slope 930 and a detune point for negative slope 940. That is, as shown in Figure 9, the reference signal 920 is curved in a similar manner to the measured signal 910. Accordingly, when a reference signal 920 value is subtracted from a corresponding measured signal 910 at a corresponding detune frequency, the net magnetometry curve peak to peak intensity contrast is reduced. The reason that the reference signal 910 curve contains information from the measured signal 910 curve is due to insufficient (laser only) polarization time for a given sensor configuration. The prior RF pulse defines the state of the measurement and, if not enough time passes between measurements, then the reference signal 920 will contain some of the "hold" data from the prior RF "sample." This will subtract from the current measured signal 910, thereby resulting in less signal overall as seen in Figure 9. Thus, to remove the prior signal information, the system would need to wait until the prior signal information is eliminated from the reference signal or operate without the reference signal, such as described herein. Prior signal information from a prior measured signal 910 (RF pulse) is cleared out via excitation from a green laser source and waiting for a period of time. This decay is exponential and tied to the power density applied from laser. However, waiting for a period of time for the prior signal information to be eliminated can decrease available bandwidth.

[0045] Figure 10 is a diagram depicting slope relative to laser polarization pulse width for a system implementing a reference signal and a system omitting the reference signal. A first slope line 1010 corresponds to a system utilizing a reference signal while a second slope line 1020 corresponds to a system without utilizing a reference signal. As shown, the second slope line 1020 has a higher slope at equivalent laser pulse widths (in microseconds) compared to the first slope line 1010 that uses a reference signal. Longer polarization pulse widths can allow for a more complete repolarization of the a magneto-optical defect center material quantum state to reduce the residual impact of previous RF excitations. In effect, this more complete polarization can allow "less dimmed" fluorescence levels to be measured more accurately rather than exhibiting residual dimming due to an earlier RF excitation that retains some NV spin +1/-1 excited states. The wider measurement range can increase the peak to peak intensity range and, therefore, optimal slope. While both unreferenced first slope line 1010 and the referenced second slope line 1020 indicate a drop off in slope with shorter polarization pulse widths, the referenced second slope line 1020 decreases more quickly than the unreferenced first slope line 1010 due to the incomplete polarization of the reference, such as the reference signal 920 of Figure 9, that is further subtracted from the measured signa, such as measured signal 910 of Figure 9. As shown, the second slope line 1020 has a slower roll-off (e.g., reduction) of slope at shorter laser pulse widths than the first slope line 1010. That is, the lase pulse widths can be reduced without a significant decrease in optimal slope values. The second slope line 1020 can achieve a smaller laser pulse width of approximately 60-70 microseconds with minimal loss in slope compared to the first slope line 1010 that reduces slope by a factor of two when the laser pulse width is reduced by a factor of four. Thus, by eliminating the need for the reference signal, the second slope line 1020 demonstrates that the system can achieve an increase in sample rate by a factor of four with minimal impact on the slope point.

[0046] Figure 11 depicts a comparison of a sensitivity of a system relative to a laser polarization pulse length for a system implementing a reference signal and a system omitting the reference signal. In the diagram shown, a first sensitivity line 1110 for the system implementing the reference signal has a lower sensitivity achievable at 10 nanoTeslas per root Hertz for a polarization pulse length of 150 microseconds. Thus, the system is limited in sampling rate based on a polarization pulse length of 150 microseconds as lower polarization pulse lengths reduce the sensitivity achievable to higher values. In comparison, a second sensitivity line 1120 for the system without the reference signal continues to increase the achievable lower sensitivity for lower polarization pulse lengths below 150 microseconds. Thus, by eliminating the reference signal, the sensitivity of the system can be improved for shorter polarization pulse lengths.

[0047] FIG. 12 depicts some implementations of a process 1200 of operating a magnetometer that utilizes a magneto-optical defect center material, such as a diamond having nitrogen vacancies. The process 1200 includes activating an RF pulse sequence (block 1202). The RF pulse sequence is done without acquiring a reference measurement, thereby reducing

measurement noise and increasing sample bandwidth by eliminating noise introduced by the reference measurement and decreasing the time between measurement acquisitions. In some implementations, a nominal ground reference measurement (block 1204) may be acquired as a simple offset relative to the ground state. The process 1200 further includes acquiring b field measurement data (block 1206). The acquisition of b field measurement data may be acquired at a faster sample rate as full repolarization of the magneto-optical defect center material is eliminated between measurements. In some implementations, the acquired b field measurement data may be processed to determine a vector of a measured b field. By removing the reference signal, a sensor can increase AC sensitivity and bandwidth.

[0048] FIG. 13 is a diagram illustrating an example of a system 1300 for implementing some aspects such as the controller. The system 1300 includes a processing system 1302, which may include one or more processors or one or more processing systems. A processor may be one or more processors. The processing system 1302 may include a general-purpose processor or a specific-purpose processor for executing instructions and may further include a machine- readable medium 1319, such as a volatile or non-volatile memory, for storing data and/or instructions for software programs. The instructions, which may be stored in a machine-readable medium 1310 and/or 1319, may be executed by the processing system 1302 to control and manage access to the various networks, as well as provide other communication and processing functions. The instructions may also include instructions executed by the processing system 1302 for various user interface devices, such as a display 1312 and a keypad 1314. The processing system 1302 may include an input port 1322 and an output port 1324. Each of the input port 1322 and the output port 1324 may include one or more ports. The input port 1322 and the output port 1324 may be the same port (e.g., a bi-directional port) or may be different ports.

[0049] The processing system 1302 may be implemented using software, hardware, or a combination of both. By way of example, the processing system 1302 may be implemented with one or more processors. A processor may be a general-purpose microprocessor, a

microcontroller, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA), a Programmable Logic Device (PLD), a controller, a state machine, gated logic, discrete hardware components, or any other suitable device that can perform calculations or other manipulations of information.

[0050] A machine-readable medium may be one or more machine-readable media, including no-transitory or tangible machine-readable media. Software shall be construed broadly to mean instructions, data, or any combination thereof, whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise. Instructions may include code (e.g., in source code format, binary code format, executable code format, or any other suitable format of code).

[0051] Machine-readable media (e.g., 1319) may include storage integrated into a processing system such as might be the case with an ASIC. Machine-readable media (e.g., 1310) may also include storage external to a processing system, such as a Random Access Memory (RAM), a flash memory, a Read Only Memory (ROM), a Programmable Read-Only Memory (PROM), an Erasable PROM (EPROM), registers, a hard disk, a removable disk, a CD-ROM, a DVD, or any other suitable storage device. Those skilled in the art will recognize how best to implement the described functionality for the processing system 1302. According to one aspect of the disclosure, a machine-readable medium is a computer-readable medium encoded or stored with instructions and is a computing element, which defines structural and functional

interrelationships between the instructions and the rest of the system, which permit the instructions' functionality to be realized. Instructions may be executable, for example, by the processing system 1302 or one or more processors. Instructions can be, for example, a computer program including code for performing methods of some of the embodiments.

[0052] A network interface 1316 may be any type of interface to a network (e.g., an Internet network interface), and may reside between any of the components shown in FIG. 13 and coupled to the processor via the bus 1304.

[0053] A device interface 1318 may be any type of interface to a device and may reside between any of the components shown in FIG. 13. A device interface 1318 may, for example, be an interface to an external device (e.g., USB device) that plugs into a port (e.g., USB port) of the system 1300.

[0054] One or more of the above-described features and applications may be implemented as software processes that are specified as a set of instructions recorded on a computer readable storage medium (alternatively referred to as computer-readable media, machine-readable media, or machine-readable storage media). When these instructions are executed by one or more processing unit(s) (e.g., one or more processors, cores of processors, or other processing units), they cause the processing unit(s) to perform the actions indicated in the instructions. In one or more implementations, the computer readable media does not include carrier waves and electronic signals passing wirelessly or over wired connections, or any other ephemeral signals. For example, the computer readable media may be entirely restricted to tangible, physical objects that store information in a form that is readable by a computer. In one or more implementations, the computer readable media is non-transitory computer readable media, computer readable storage media, or non-transitory computer readable storage media. [0055] In one or more implementations, a computer program product (also known as a program, software, software application, script, or code) can be written in any form of programming language, including compiled or interpreted languages, declarative or procedural languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, object, or other unit suitable for use in a computing

environment. A computer program may, but need not, correspond to a file in a file system. A program may be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub programs, or portions of code). A computer program may be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network.

[0056] While the above discussion primarily refers to microprocessor or multi-core processors that execute software, one or more implementations are performed by one or more integrated circuits, such as application specific integrated circuits (ASICs) or field programmable gate arrays (FPGAs). In one or more implementations, such integrated circuits execute instructions that are stored on the circuit itself.

[0057] In some aspects, some embodiments directed to magnetic band-pass filters for signals in magnetic communications and anomaly detection using diamond nitrogen-vacancy (DNV). In some aspects, some embodiments may be used in various markets, including for example and without limitation, advanced sensors and magnetic communication systems markets.

[0058] The description is provided to enable any person skilled in the art to practice the various embodiments described herein. While some embodiments have been particularly described with reference to the various figures and configurations, it should be understood that these are for illustration purposes only and should not be taken as limiting the scope of the subject technology.

[0059] There may be many other ways to implement. Various functions and elements described herein may be partitioned differently from those shown without departing from the scope of the subject technology. Various modifications to these embodiments may be readily apparent to those skilled in the art, and generic principles defined herein may be applied to other embodiments. Thus, many changes and modifications may be made by one having ordinary skill in the art, without departing from the scope of the subject technology.

[0060] A reference to an element in the singular is not intended to mean "one and only one" unless specifically stated, but rather "one or more." The term "some" refers to one or more. Underlined and/or italicized headings and subheadings are used for convenience only, do not limit the subject technology, and are not referred to in connection with the interpretation of the description of the subject technology. All structural and functional equivalents to the elements of the various embodiments described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and intended to be encompassed by the subject technology. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the above description.