Multi-state rydberg electrometry using an optical frequency comb

Abstract

A method of detecting electromagnetic fields using electromagnetically-induced absorption includes the steps of irradiating a quantum system with a coupling laser, wherein the coupling laser is an optical frequency comb; irradiating the quantum system with a probe laser; exposing the quantum field to an electromagnetic field; measuring transmittance of the probe laser through the quantum system; and determining the exposed electromagnetic field based on the measured transmittance of the probe laser.

Description

[0001] MULTI-STATE RYDBERG ELECTROMETRY USING AN OPTICAL FREQUENCY COMB

[0002] Related Applications

[0003] This application claims the benefit of U.S. Provisional Patent Application Serial No. 63 / 691 ,370 (filed September 6, 2024), which is herein incorporated by reference in its entirety.

[0004] Federally-Sponsored Research and Development

[0005] This invention was made with United States Government support from the National Institute of Standards and Technology (NIST), an agency of the United States Department of Commerce. The Government has certain rights in this invention.

[0006] Copyright Notice

[0007] This patent disclosure may contain material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure as it appears in the U.S. Patent and Trademark Office patent file or records, but otherwise reserves any and all copyright rights.

[0008] Field of Invention

[0009] The present invention relates generally to Rydberg electrometry, and more particularly to an optical frequency comb allowing for rapid measurements across states and frequencies.

[0010] Background

[0011] Rydberg electrometry allows for Sl-traceable, calibration-free measurements of electric fields. Summary of Invention

[0012] However, these measurements are generally limited to single Rydberg state which leads to a narrow radiofrequency detection bandwidth. Herein described is a method using an optical frequency comb to generate numerous Rydberg atoms corresponding to different states, allowing for rapid measurements across states and frequencies.

[0013] According to an aspect of the invention, a method of detecting electromagnetic fields using electromagnetically-induced absorption includes the steps of irradiating a quantum system with a coupling laser, wherein the coupling laser is an optical frequency comb; irradiating the quantum system with a probe laser; exposing the quantum field to an electromagnetic field; measuring transmittance of the probe laser through the quantum system; and determining the exposed electromagnetic field based on the measured transmittance of the probe laser.

[0014] Optionally, the method also includes the step of irradiating the quantum system with a dressing laser.

[0015] Optionally, the probe laser is a 895 nm laser.

[0016] Optionally, the coupling laser is a 2235 nm laser.

[0017] Optionally, the dressing laser is a 636 nm laser.

[0018] Optionally, the electromagnetic field includes radio-waves.

[0019] Optionally, the electromagnetic field includes microwaves.

[0020] Optionally, the quantum system includes Rydberg atoms.

[0021] Optionally, the method also includes the step of generating the coupling laser by passing a seed laser through an electro-optic modulator.

[0022] Optionally, the method also includes the step of generating the coupling laser with an optical parametric oscillator.

[0023] Optionally, the step of generating the coupling laser includes selecting a comb spacing and span.

[0024] Optionally, the step of generating the coupling laser includes selecting a comb spectral range.

[0025] Optionally, the method includes the step of combining the coupling laser and the probe laser and passing the combined laser through a vapor cell containing the quantum system. Optionally, the dressing laser is counter-propagated with respect to the coupling laser and the probe laser, thereby reducing Doppler effect.

[0026] Optionally, the method also includes the steps of spectrally filtering the probe laser to remove light from the coupling laser; and measuring the filtered probe laser on a balanced photo-diode, thereby enabling near shot-noise-limited detection.

[0027] According to another aspect of the invention, an electromagnetic field detector includes a coupling laser configured to irradiate a quantum system, wherein the coupling laser produces an optical frequency comb; a probe laser configured to irradiate the quantum system; a vapor cell containing the quantum system; a photodiode configured to measure laser light transmitted through the vapor cell; and a computer configured to infer characteristics of an electromagnetic field acting on the quantum system in the vapor cell.

[0028] Optionally, the coupling laser includes a seed laser and an electro-optic modulator configured to modulate a beam from the seed laser into the optical frequency comb.

[0029] Optionally, the electromagnetic field detector also includes a dressing laser configured to irradiate the quantum system.

[0030] Optionally, the dressing laser beam is configured to counter-propagate with respect to beams of the coupling laser and the probe laser, thereby reducing Doppler effect.

[0031] Optionally, the vapor cell includes Rydberg atoms.

[0032] Optionally, the electromagnetic field detector includes an optical frequency comb on the probe laser.

[0033] The foregoing and other features of the invention are hereinafter described in greater detail with reference to the accompanying drawings.

[0034] Brief Description of the Drawings

[0035] FIG. 1 shows (a) three-photon excitation to the 75 P3 / 2 state in a Rydberg manifold utilizing 895 nm (probe), 636 nm (dressing), and 2235 nm (coupling) optical fields; (b) expanded view of the Rydberg manifold which shows the coupling laser optical frequency comb which connects the seven different Rydberg states which are centered around 75 P3 / 2; and (c) energy layout of nearby Rydberg states and some possible RF transition frequencies between the nPs / 2 states and nearby S and D Rydberg states.

[0036] FIG. 2 shows (a) mid-infrared comb generation schematic and (b) measurement system schematic. An electro-optic frequency comb with a tooth spacing of 18 GHz is produced on the 1068 nm pump laser with an electro-optic (specifically a Mach-Zehnder) modulator. This comb then pumps an optical parametric oscillator to produce a 2235 nm optical frequency comb which serves as the coupling laser. This comb is combined with the 895 nm probe laser and passed through a cesium vapor cell. The 636 nm dressing laser is counter-propagated through the cell. The probe light passing through the cell is then filtered (to remove the coupling light) before being recorded on a balanced photodetector.

[0037] FIG. 3 shows (a) a sample electromagnetically induced absorption (EIA) spectrum showing the peaks corresponding to the different Rydberg states as the coupling laser is scanned; (b) a response of the 73 P3 / 2 Rydberg state as the RF power of an applied 9.907 GHz field is increased; and (c) a corresponding 73 P3 / 2 response as the applied RF frequency is varied near the Rydberg resonance while the applied RF power is fixed to -5 dBm.

[0038] FIG. 4 shows a set of plots in which each panel shows the response of given Rydberg states for a range of applied radiofrequencies. Each row corresponds to a particular Rydberg state (labeled on the right) and each column corresponds to different applied radiofrequencies. In each panel the y-axis is the coupling laser detuning used to observe the given Rydberg state and the x-axis is a scan of the RF frequency centered on the atomic resonance with a span of 40 MHz. The panels in which a response is expected have been highlighted.

[0039] FIG. 5 shows a schematic of an exemplary computer for performing exemplary methods and / or parts thereof.

[0040] Detailed Description

[0041] Rydberg atoms are touted as a means to measure electric fields from DC to THz, but unlike classical antennas that continuously monitor the entire spectrum, Rydberg atoms are limited to a narrow 30 MHz span around a resonance of two Rydberg states. This can be extended to a few hundred megahertz by utilizing Rydberg engineering techniques, but this still does not bridge the gap for continuous tuning and measurement of several incoming radiofrequency (RF) signals. For Rydberg atoms to compete with classical receivers, a method for rapid measurement of different Rydberg states is required. Presented herein is an approach utilizing a frequency comb to concurrently investigate numerous Rydberg states and expand the range of the Rydberg atom sensor's tuning bandwidth.

[0042] By utilizing an electro-optic frequency comb to pump an optical parametric oscillator, an optical frequency comb in the mid-infrared spectral region can be generated with up to 80 mW of power in each comb tooth. These high comb tooth powers have been shown to enable the rapid generation of numerous different Rydberg states, paving the way for rapid electrometry measurements across a wide frequency band. This method allows for the sensor to cover a frequency range of 1 to 40 GHz or more, which can be easily readjusted by tuning a frequency comb or laser detuning within the laser's free spectral range with fast current control.

[0043] The ability to rapidly produce Rydberg atoms corresponding to different Rydberg states allows for the rapid and orthogonal detection of electric fields in different radiofrequency ranges. This allows for wideband detection as well as spectral multiplexing. Whereas conventional approaches are generally limited to a single Rydberg state and therefore a narrow detectable range of radiofrequency fields.

[0044] Described herein is an implementation of this approach, where a frequency comb is placed on the coupling laser of a three photon Rydberg electrometer. However, it is noted that that exemplary embodiments include a wide variety of other Rydberg electrometers (two photon, four photon, other versions of three photon, e.g.). Exemplary embodiments utilize an optical frequency comb to rapidly prepare multiple Rydberg states. In addition, as noted herein, there are a range of protocols which could be employed for information transfer using this approach. The two mentioned herein (frequency hopping shared spectrum, FHSS, and orthogonal frequency division multiplexing, OFDM) are not limiting examples but rather the invention is applicable to the wide range of potential protocols.

[0045] In the exemplary embodiment described herein, the coupling frequency comb is dithered to allow for a facile readout, however, this does not have to be the case, and there are a variety of other implementations in which other lasers could be dithered or a multiplexed readout employed, for example.

[0046] It is noted that the comb generation approach described herein (i.e. , spectral translation of an electro-optic comb to the mid-infrared with optical parametric oscillation) is not the only way that an optical frequency comb could be generated for use as the coupling laser in Rydberg electrometry. Rather, all of the traditional comb generation approaches (mode-locked lasers, electro-optic combs, microcombs, etc.) could be applicable as well as the multitude of methods for spectral translation of these combs.

[0047] Finally, it is noted that these results are not purely limited to Rydberg electrometry. Rather, exemplary methods of utilizing a frequency comb to rapidly excite atoms (or molecules) to selected excited states could be utilized for a wide range of different applications in sensing (and beyond). Possible other applications include magnetometry, atomic clocks, pump-probe spectroscopy. Time resolved approaches which leverage the rapid possible measurement speeds of optical frequency combs are also possible.

[0048] Optical frequency combs have been transformative in wide ranging fields such as time transfer, astronomy, and remote sensing. These advancements have largely leveraged the exquisite frequency accuracy that combs can provide as well as their wide spectral bandwidth. However, their low power per comb tooth (generally microwatts or even nanowatts) has proven limiting in some applications. A new approach for spectral translation of electro-optic frequency combs using an optical parametric oscillator (OPO) has been recently demonstrated. Critically, this method allows for highly coherent spectral translation from the near-infrared to the important mid-infrared while also offering exceptionally high power per comb tooth (up to 300 mW).

[0049] Exemplary methods may utilize this frequency agile optical frequency comb as the coupling laser in a three-photon Rydberg electrometry instrument, allowing for the preparation of as many as seven Rydberg states rapidly. The seven individual states can serve as orthogonal RF channels, allowing for rapid and highly sensitive detection of a multitude of RF tones across a range of 1 GHz to 40 GHz, limited only by available RF sources and horn antennas. The multi-state Rydberg receiver described herein utilizes three-photon excitation to generate and probe Rydberg states in cesium (Cs) atoms as shown in FIG. 1. The three-photon configuration leads to a reduced Doppler broadening due to the wavelengths of the various optical fields and therefore a higher theoretical maximum sensitivity. Although it is noted that the methods described herein are also applicable to more traditional two-photon approaches.

[0050] The coherent multi-photon process known as electromagnetically-induced absorption (EIA) allows for probing highly excited Rydberg states with higher precision than other methods such as ionization, electron beam ionization, and direct absorption measurements. In the exemplary three-photon process, an 895 nm probe laser, a 636 nm dressing laser, and a 2235 nm coupling optical frequency comb may be used in a successive excitation up to the Rydberg state(s) of interest, thus generating a coherent ensemble of atoms. The EIA is a result of this coherence and readout of the probe laser is a measure of the coherence between the ground state and the first excited state. The dressing and coupling laser modify this coherence through their interactions with the 9S intermediate state and the Rydberg state. This projection allows for measurements of Rydberg state(s) of interest by measuring the probe laser transmission. Similarly, the modification of the Rydberg state by an RF field also effects the probe laser transmission.

[0051] As used herein, a coupling laser means a laser used to manipulate the atomic system by inducing transitions between energy levels within the atoms. A coupling laser typically interacts with the atoms at specific wavelengths that match the atomic transition frequencies. A coupling laser's interaction with the atoms can change the atomic population distribution, for example, by transferring atoms from the ground state to an excited state.

[0052] As used herein, a dressing laser means a laser used to alter the energy levels of the atoms, creating a new energy level structure for interaction with other lasers. The dressing laser's effect is not to induce transitions directly, but to change the energy levels themselves, often through the Stark effect or other forms of laser- induced interactions. This can be used to modify the interaction between the atoms and other lasers, such as the probe laser. The dressing laser is typically tuned to a specific wavelength to interact with the atoms at the desired energy levels. As used herein, a probe laser means a laser used to read out the atomic state or measure the effects of the coupling and / or dressing lasers. A probe laser can be used to detect the presence of atoms in specific energy levels or to measure the coherence of the atomic state. A probe laser's interaction with the atoms can reveal information about the atomic population, coherence, and other properties affected by the coupling and dressing lasers. A probe laser is typically tuned to a specific wavelength to interact with the atoms and provide information about their state.

[0053] An optical parametric oscillator (OPO) may be used to produce the frequency agile, mid-infrared optical frequency comb which may serve as the coupling laser (see FIG. 2). To generate this optical frequency comb, the (e.g., 1068 nm) OPO seed laser 210 may first be passed through a modulator (e.g., a dual-drive Mach- Zehnder modulator) 220. By driving both sides of the modulator with an 18 GHz RF tone, an optical frequency comb is produced with a comb spacing of 18 GHz. This comb spacing roughly matches the separation of the selected Rydberg states shown in FIG. 1 (b). The comb tooth amplitudes may then be flattened by adjusting the phase shift and RF power between the two arms of the Mach-Zehnder modulator. This comb may then be amplified (to, e.g., about 10 W) by an amplifier 230 before serving as the pump laser for a commercial, singly resonant, continuous-wave OPO 240. The OPO may include a periodically poled lithium niobate (PPLN) 242.

[0054] Because only the signal beam is resonant within the OPO cavity, the optical frequency comb on the pump beam would be efficiently and coherently transferred on to the mid-infrared idler beam. Of great benefit, this approach allows for the generation of a high power, frequency agile comb, where the comb spacing and span are entirely flexible and can be set to well match an arbitrary set of Rydberg levels. In addition, the output comb can be tuned over a spectral range between 2200 nm and 4000 nm. For the exemplary measurements, it was tuned to 2235 nm, where the comb had a total power >2 W and seven strong comb teeth which had an average power per tooth near 300 mW. This power per comb tooth is more than sufficient to allow for multi-state Rydberg preparation.

[0055] The optical frequency comb coupling laser may then be combined with the (e.g., 895 nm) probe laser 250 and passed through a133Cs filled vapor cell 260. The (e.g., 636 nm) dressing laser 270 may be counter-propagated through the cell in order to reduce the Doppler effect. The transmitted probe beam may then be spectrally filtered (in order to remove the coupling light) and measured on a balanced photo-diode 280, allowing for near shot-noise-limited detection and determ ination / characterization by an oscilloscope or computer 290 of applied / external electromagnetic waves (herein show, for example, to be created by one or more horn antennas.

[0056] In an embodiment, the OPO pump laser (and thus the entire coupling optical frequency comb) may be scanned over a range of 2 GHz in order to excite each Rydberg state individually, as shown in FIG. 3 (a). The detuning of each state corresponds to the energy difference between the nearest comb tooth and the state in question (as defined in Table 1). The peaks in the spectrum show the seven Rydberg states which can be prepared by the optical frequency comb coupling laser. It is noted that the reverse configuration can also be performed. By locking the coupling laser and tuning the comb spacing and tooth amplitudes, fast switching between the distinct Rydberg states can be achieved and unique demodulation schemes may be employed to receive information from the various frequency ranges rapidly.

[0057] Table 1. Energy separation of the different Rydberg P3 / 2 states in the manifold. Also shown are the relative comb spacing and detunings of these states from the nearest comb teeth.

[0058] Armed with this multi-state readout, this approach can be utilized to observe a broad range of effects on the different Rydberg states (see Fig. 1 (c)) being probed. For example, the independent response of select states to particular RF fields, the splitting of the Rydberg state resonances for calibration purposes, and even a Stark shift when the applied field is strong enough may be observed. Figure 3(b) shows the Autler-Townes splitting as the power of the signal generator is increased. By extracting the splitting, the field strength of the incident field can be determined by, where h is the reduced Planck constant, E is the electric field, Ameas is the measured Rydberg state splitting, and / ,yis the transition dipole moment between the two Rydberg states. For example, at -5 dBm of applied RF, a splitting of 30 MHz is observed. The transition dipole moment for this transition is 2480 e-1ao-1, where e is the electron charge and ao is the Bohr radius. In these experiments all the optical fields the RF fields are co-polarized; as such 0.48989 may be used as the angular part of the dipole moment. For this case, the field measured by the atoms was 0.95 V / m.

[0059] Another effect which can be observed are avoided crossings as the frequency of the applied RF is scanned, shown by Fig. 3 (c). The usual AT behavior with RF detuning is observed, in that there are three main effects on the observed splitting of the electromagnetically induced transparency (EIT) signal

[0044] : (1) the two peaks of the EIT signal are nonsymmetric, (2) the separation between the two AT peaks increases with RF detuning, and (3) one peak is pulled to the zero detuning location of the coupling laser. In this case, the splitting is proportional to the generalized Rabi frequency (Ameas = / £lRP+2RP), where ORF is proportional to the field strength and AR is the detuning of the RF from the atomic resonance. As a broad scan in frequency is performed, these avoided crossings can be used to identify the location of the different RF Rydberg transitions.

[0060] The unique broadband nature of the present method becomes apparent when different RF fields are applied to the atoms. Exemplary embodiments may use three horn antennas to apply RF fields ranging from 1 GHz to 40 GHz. The lower RF bound may be set by the atomic transitions between states in this region of the Rydberg manifold while the upper bound may be set by the available RF sources and antennas. It is noted that the use of higher frequency RF sources and antennas should allow for a significantly wider measurable RF range.

[0061] For these measurements, RF frequencies over 20-MHz-wide ranges which were centered on Rydberg transitions between 1 GHz and 40 GHz were applied (see FIG. 4). For example, the first column in FIG. 4 shows the response of the seven states to a field ranging from 1.440 GHz to 1 .480 GHz. For each column in FIG. 4, the panel where a response to the RF field is expected has been highlighted. Avoided crossings were observed, caused by the mixing of the optically excited Rydberg states and the Rydberg state coupled by the RF field. Importantly, since each of the transition frequencies in this section of the Rydberg manifold are separated by over 50 MHz, a single RF frequency is expected to only interact with a single Rydberg state, thus allowing for complete orthogonality. Experimentally this is what has been observed, where the measured response to the RF fields in a multitude different frequency bands up to 40 GHz exhibits no effects of cross-talk between Rydberg states. The orthogonal nature is crucial for various communication protocols including frequency hopping shared spectrum (FHSS) and orthogonal frequency domain multiplexing (OFDM).

[0062] FHSS is a protocol that relies on frequency-agile sensors that can quickly switch between frequency bands in order to avoid jamming or perform signal interception. However, the bands are generally limited by the bandwidth of the antenna being utilized for reception to at most a few of gigahertz. Critically, with the present frequency comb-based approach, it should be possible to switch between vastly different operational bands and therefore significantly improve the performance of this protocol for Rydberg sensing.

[0063] Orthogonal frequency division multiplexing (OFDM) is another protocol which relies upon spreading information over several frequency bands simultaneously. In this way information is simultaneously sent over multiple carriers, and each carrier must be separately demodulated. For FHSS where the frequency comb is utilized, it should be possible to separate the carriers subsequently by tuning the comb frequency or laser detuning. While the FHSS protocol can be achieved by utilizing Stark shifting measurements, OFDM requires that all of the carriers be received simultaneously and typically have the same base-band modulation. This means that if a single probe was used for readout, all the base-bands would interfere if Stark shifting measurements were utilized. This is where the use of the frequency comb method can separate the RF carriers for simultaneous broadband detection.

[0064] The use of an optical frequency comb as the coupling laser for Rydberg electrometry enables rapid and orthogonal measurements over a range of states and therefore radiofrequencies. The increased capabilities made possible by this approach are expected to have an extensive impact on communications and sensing. It is noted that a classical receiver would require numerous different antennas and substantial down-conversion hardware to receive the same signals that an exemplary comb-enabled Rydberg receiver can readily record. Further, recording radiofrequencies from 1 GHz to 100 GHz is readily possible, whereby the direct conversion nature of Rydberg atoms is anticipated to be truly enabling as telecommunications continue to push the limits of existing electronic hardware.

[0065] Although as described herein for clarity as using an optical comb on the coupling laser for rapidly switched detection, other configurations are also possible. For example, simultaneous detection could be achieved by placing additional combs on the dressing and probe lasers in a three photon system or by placing a comb on the probe laser in a two photon system. Placing a comb on the probe laser compensates the energy, giving access to the full Doppler width. The probe may, in this embodiment, have a comb that matches the detunings present on the scan of the coupling laser. This approach would allow for simultaneous state preparation and the protocols such as OFDM

[0066] It should be understood that the calculations and determinations used by exemplary embodiments may be performed by any suitable computer system, such as that diagrammatically shown in FIG. 5. Data is entered into system 500 via any suitable type of user interface 516, and may be stored in memory 512, which may be any suitable type of computer readable and programmable memory and is preferably a non-transitory, computer readable storage medium. Calculations are performed by processor 514, which may be any suitable type of computer processor and may be displayed to the user on display 518, which may be any suitable type of computer display. Processor 514 may be associated with, or incorporated into, any suitable type of computing device, for example, a personal computer or a programmable logic controller. The display 518, the processor 514, the memory 512 and any associated computer readable recording media are in communication with one another by any suitable type of data bus, as is well known in the art.

[0067] Examples of computer-readable recording media include non-transitory storage media, a magnetic recording apparatus, an optical disk, a magneto-optical disk, and / or a semiconductor memory (for example, RAM, ROM, etc.). Examples of magnetic recording apparatus that may be used in addition to memory 512, or in place of memory 512, include a hard disk device (HDD), a flexible disk (FD), and a magnetic tape (MT). Examples of the optical disk include a DVD (Digital Versatile Disc), a DVD-RAM, a CD-ROM (Compact Disc-Read Only Memory), and a CD-R (Recordable)ZRW. It should be understood that non-transitory computer-readable media include all computer-readable media except for a transitory, propagating signal.

[0068] The processes described herein may be embodied in, and fully automated via, software code modules executed by a computing system that includes one or more general purpose computers or processors. The code modules may be stored in any type of non-transitory computer-readable medium or other computer storage device. Some or all the methods may alternatively be embodied in specialized computer hardware. In addition, the components referred to herein may be implemented in hardware, software, firmware, or a combination thereof.

[0069] Many other variations than those described herein will be apparent from this disclosure. For example, depending on the embodiment, certain acts, events, or functions of any of the algorithms described herein can be performed in a different sequence, can be added, merged, or left out altogether (e.g., not all described acts or events are necessary for the practice of the algorithms). Moreover, in certain embodiments, acts or events can be performed concurrently, e.g., through multithreaded processing, interrupt processing, or multiple processors or processor cores or on other parallel architectures, rather than sequentially. In addition, different tasks or processes can be performed by different machines and / or computing systems that can function together.

[0070] Any logical blocks, modules, and algorithm elements described or used in connection with the embodiments disclosed herein can be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, and elements have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. The described functionality can be implemented in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the disclosure.

[0071] The various illustrative logical blocks and modules described or used in connection with the embodiments disclosed herein can be implemented or performed by a machine, such as a processing unit or processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A processor can be a microprocessor, but in the alternative, the processor can be a controller, microcontroller, or state machine, combinations of the same, or the like. A processor can include electrical circuitry configured to process computer-executable instructions. In another embodiment, a processor includes an FPGA or other programmable device that performs logic operations without processing computerexecutable instructions. A processor can also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. Although described herein primarily with respect to digital technology, a processor may also include primarily analog components. For example, some or all of the signal processing algorithms described herein may be implemented in analog circuitry or mixed analog and digital circuitry. A computing environment can include any type of computer system, including, but not limited to, a computer system based on a microprocessor, a mainframe computer, a digital signal processor, a portable computing device, a device controller, or a computational engine within an appliance, to name a few.

[0072] The elements of a method, process, or algorithm described in connection with the embodiments disclosed herein can be embodied directly in hardware, in a software module stored in one or more memory devices and executed by one or more processors, or in a combination of the two. A software module can reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of non- transitory computer-readable storage medium, media, or physical computer storage known in the art. An example storage medium can be coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium can be integral to the processor. The storage medium can be volatile or nonvolatile.

[0073] While one or more embodiments have been shown and described, modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustrations and not limitation. Embodiments herein can be used independently or can be combined.

[0074] All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other. The ranges are continuous and thus contain every value and subset thereof in the range. Unless otherwise stated or contextually inapplicable, all percentages, when expressing a quantity, are weight percentages. The suffix (s) as used herein is intended to include both the singular and the plural of the term that it modifies, thereby including at least one of that term (e.g., the colorant(s) includes at least one colorants). Option, optional, or optionally means that the subsequently described event or circumstance can or cannot occur, and that the description includes instances where the event occurs and instances where it does not. As used herein, combination is inclusive of blends, mixtures, alloys, reaction products, collection of elements, and the like.

[0075] As used herein, a combination thereof refers to a combination comprising at least one of the named constituents, components, compounds, or elements, optionally together with one or more of the same class of constituents, components, compounds, or elements.

[0076] All references are incorporated herein by reference.

[0077] The use of the terms “a,” “an,” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. It can further be noted that the terms first, second, primary, secondary, and the like herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. It will also be understood that, although the terms first, second, etc. are, in some instances, used herein to describe various elements, these elements should not be limited by these terms. For example, a first current could be termed a second current, and, similarly, a second current could be termed a first current, without departing from the scope of the various described embodiments. The first current and the second current are both currents, but they are not the same condition unless explicitly stated as such.

[0078] The modifier about used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., it includes the degree of error associated with measurement of the particular quantity). The conjunction or is used to link objects of a list or alternatives and is not disjunctive; rather the elements can be used separately or can be combined together under appropriate circumstances.

[0079] Although the invention has been shown and described with respect to a certain embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a "means") used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e. , that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.

Claims

Claims1 . A method of detecting electromagnetic fields using electromagnetically- induced absorption, the method comprising the steps of: irradiating a quantum system with a coupling laser, wherein the coupling laser is an optical frequency comb; irradiating the quantum system with a probe laser; exposing the quantum field to an electromagnetic field; measuring transmittance of the probe laser through the quantum system; and determining the exposed electromagnetic field based on the measured transmittance of the probe laser.

2. The method of claim 1 , further comprising the step of: irradiating the quantum system with a dressing laser.

3. The method of claim 1 , wherein the probe laser is a 895 nm laser.

4. The method of claim 1 , wherein the coupling laser is a 2235 nm laser.

5. The method of claim 2, wherein the dressing laser is a 636 nm laser.

6. The method of claim 1 , wherein the electromagnetic field includes radio-waves.

7. The method of claim 1 , wherein the electromagnetic field includes microwaves.

8. The method of claim 1 , wherein the quantum system includes Rydberg atoms.

9. The method of claim 1 , further comprising the step of generating the coupling laser by passing a seed laser through an electro-optic modulator.

10. The method of claim 1 , further comprising the step of generating the coupling laser with an optical parametric oscillator.

11. The method of claim 1 , wherein the step of generating the coupling laser includes selecting a comb spacing and span.

12. The method of claim 1 , wherein the step of generating the coupling laser includes selecting a comb spectral range.

13. The method of claim 1 , further comprising the step of combining the coupling laser and the probe laser and passing the combined laser through a vapor cell containing the quantum system.

14. The method of claim 2, wherein the dressing laser is counterpropagated with respect to the coupling laser and the probe laser, thereby reducing Doppler effect.

15. The method of claim 1 , further comprising the steps of: spectrally filtering the probe laser to remove light from the coupling laser; and measuring the filtered probe laser on a balanced photo-diode, thereby enabling near shot-noise-limited detection.

16. An electromagnetic field detector comprising: a coupling laser configured to irradiate a quantum system, wherein the coupling laser produces an optical frequency comb; a probe laser configured to irradiate the quantum system; a vapor cell containing the quantum system; a photo-diode configured to measure laser light transmitted through the vapor cell; and a computer configured to infer characteristics of an electromagnetic field acting on the quantum system in the vapor cell.

17. The electromagnetic field detector of claim 16, wherein the coupling laser includes a seed laser and an electro-optic modulator configured to modulate a beam from the seed laser into the optical frequency comb.

18. The electromagnetic field detector of claim 16, further comprising: a dressing laser configured to irradiate the quantum system.

19. The electromagnetic field detector of claim 18, wherein the dressing laser beam is configured to counter-propagate with respect to beams of the coupling laser and the probe laser, thereby reducing Doppler effect.

20. The electromagnetic field detector of claim 16, wherein the vapor cell includes Rydberg atoms.

21. The electromagnetic field detector of claim 16, further comprising an optical frequency comb on the probe laser.

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