Sensitive THZ detector using field ionization of rydberg atoms

Abstract

Disclosed herein in are a method and an electrometer sensor for sensing an electromagnetic signal based on changing states of atoms in an atomic vapor. The method includes irradiating the atomic vapor within a vacuum cell with a laser; exciting the atoms into a first Rydberg state; applying a voltage bias between a first electrode and a second electrode; transitioning the atoms from the first Rydberg state to a second Rydberg state by the electromagnetic signal; ionizing the atoms by sweeping the voltage bias between the first electrode and the second electrode; generating an electron signal that is representative of a population of atoms in at least one of the first Rydberg state and the second Rydberg state; determining the electron signal at the second electrode by an ion detector; and determining a strength of the electrical field of the electromagnetic signal.

Description

SENSITIVE THZ DETECTOR USING FIELD IONIZATION OF RYDBERG ATOMSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 774,914, filed March 20, 2025, the contents of which are hereby incorporated by reference in their entirety.BACKGROUND

[0002] Electromagnetic radiation spans, inter alia, frequencies in the range of several hundreds of GHz to the THz levels. Sensors that are capable of sensing such high frequencies of electromagnetic field are typically based on atomic spectroscopy, which requires a precisely controlled equipment for proper operation. Some examples of the platforms that may use these sensors are the Department of Defense (DoD) sensor systems, such as UAVs, aircraft pods, and ground-based receivers. Accordingly, systems and methods capable of sensing electromagnetic radiation in THz range with enhanced stability and reliability in harsh conditions are still needed.

[0003] Direct detection of THz and sub-THz radiation is commonly implemented using ultrawideband photodiodes like Schottky Barrier Diodes paired with high-gain antennas or integrated onto CMOS as antenna-coupled transistor detectors, where an integrated antenna connects to a MOSFET, enabling self-rectification if the device channel is long enough. THz detectors based on Rydberg atoms can be at least five orders of magnitude more sensitive than the conventional electronic sensors described above and are a self-calibrating SI traceable probe.

[0004] These sensors currently use optical detection to infer the strength of a resonant microwave or THz field by measuring the Autler-Townes splitting it induces in a ladder-type electromagnetically-induced transparency (EIT) spectrum. Since this technique measures a small dip in laser absorption on a large background, the sensitivity of this approach is fundamentally limited by photon shot noise and Doppler shifts in a thermal vapor.

[0005] Existing THz detection methods face a fundamental tradeoff --conventional electronic detectors (e g., Schottky diode receivers) are robust and simple but lack thenecessary sensitivity, while atomic electrometers provide orders of magnitude higher sensitivity but rely on fragile spectroscopic techniques that limit real-world deployment. As such, there is a need for robust THz frequency sensors with higher degrees of sensitivity.BRIEF SUMMARY

[0006] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0007] The Rydberg atom ionization sensor (RAISE) is a compact, room-temperature, vapor-cell-based Rydberg electrometer designed for high-sensitivity electric field detection in the -500 GHz- 1 5 THz range. Its sensitivity derives from the large dipole moments of highly excited Rydberg states, which enable precise measurement of electric fields via field-induced transitions between Rydberg levels. When exposed to an incident THz field, atoms in the vapor cell undergo resonant transitions between adjacent Rydberg states separated by the incident photon energy. The population distribution of the final states may then be determined using state-selective field ionization (SFI): a fast-ramping electric field ionizes different Rydberg levels at distinct thresholds, and the released electrons are detected via a microchannel plate (MCP). By analyzing the time-dependent ionization signal, we extract the population distribution of final states, allowing us to infer the electric field strength at the corresponding resonant frequencies. The Rydberg atom ionization sensor can deliver robust, high-sensitivity quantum electrometry in the THz frequency range for sensing applications, including long-range radar and passive THz detection.

[0008] The RAISE sensor transitions from spectroscopic detection to a direct ionizationbased readout, significantly improving robustness while maintaining atomic-level sensitivity. This shift removes the need for frequency-scanned probe lasers, reducing system complexity and enabling reliable, high sensitivity THz detection in operational environments.

[0009] The RAISE sensor replaces EIT-based readout with state-selective field ionization (SFI) detection, eliminating the need for high-precision laser frequency scanning and reducing background shot noise. The disclosed method directly detects ionization eventsfrom Rydberg states, offering a higher signal -to-noise ratio and greater robustness in noisy environments. By using a fast-ramping electric field to ionize atoms, sub-nV / cm / vHz sensitivity and high sampling rates (-10 kHz) may be achieved, limited only by atomic diffusion. While the blackbody ionization rate of excited Rydberg states introduces a background signal, it is orders of magnitude lower than optical detection backgrounds, making it easier to isolate the RF-induced transitions. Additionally, SFI detection simplifies system integration, as it removes the need for actively stabilized probe lasers and complex optical alignment.

[0010] The sensitivity of the RAISE sensor is fundamentally limited by electron shot noise in the ionization detection process, the blackbody ionization background of the Rydberg states used, and the transition dipole strength of the Rydberg transitions sensitive to the field. Assuming a rubidium vapor cell with a density of 1011 atoms / cm3 and a 1 cm3 detection volume, exciting 1% of the vapor yields N=109 Rydberg atoms per measurement cycle. In the limit low-field limit, the transition probability is given by,where dtransis the transition dipole matrix element for the THz-driven transition, ETHzis the electric field strength, and tintis the interaction time with the sensed field. The expected signal electron count for an MCP detector efficiency,? / , is Nsig= T]N ^DTRANSE™Z~INT-^, whilethe background is dominated by blackbody autoionization and MCP dark current, givenby ^bkg = TJN^- + v ith typical values (tj = 0.6, ibbr= 2 ms, xint= 10 us. Tdet::::50 ns, dtrans:::1.2 E -26 to 2.7 E -26 C*m), we estimate the shot-noise limited SNR for detecting a 1 nV / cm THz field to be 0.3-1.3 per measurement cycle. This measurement could be repeated at a rate of 10 kHz, providing enough time for thermal atoms to diffuse across the interaction region.

[0011] In some embodiments, 200 V7m electric field noise in the 0.2 - 40 GHz range should not have a substantial effect on the measured signal. Fields at these frequencies may cause unwanted transitions out of our initial Rydberg state, but the resulting stray population should be in energy levels more than 400 GHz detuned from the target states detected in the ionization ramp.

[0012] Magnetic fields of ~mT can cause ~20 MHz Zeeman shifts in atomic spectra. This can shift the resonance of the transition to populate the initial Rydberg state, but driving this transition at 100 ns should power broaden the transition to approximately the same width. Further excitation broadening could be achieved by chirping the two-photon detuning during excitation for rapid adiabatic passage or similar techniques.

[0013] The system may require frequency-stabilized lasers to operate, as vibrations present the greatest risk. Vibrations may be mitigated by eliminating the need to scan the probe laser to detect the signal; nevertheless, the laser frequencies need to be stabilized to within the power-broadened linewidth of the Rydberg transition for the device to work. The availability of distributed Bragg reflector lasers, which offer high tunability and narrow linewidths without external cavities, may further mitigate this issue for the one or more lasers.

[0014] Disclosed herein is a method for sensing an electromagnetic signal based on changing states of atoms in an atomic vapor, the method comprising: irradiating the atomic vapor within a vacuum cell with a laser; by irradiating the atomic vapor, exciting the atoms of the atomic vapor into a first Rydberg state; applying a voltage bias between a first electrode and a second electrode, wherein the atomic vapor is at least partially confined between the first electrode and the second electrode; transitioning the atoms of the atomic vapor from the first Rydberg state to a second Rydberg state by the electromagnetic signal; ionizing the atoms of the atomic vapor by sweeping the voltage bias between the first electrode and the second electrode; by ionizing the atoms, generating an electron signal that is representative of a population of atoms in at least one of the first Rydberg state and the second Rydberg state; determining the electron signal at the second electrode by an ion detector; and based on the electron signal, determining a strength of the electrical field of the electromagnetic signal.

[0015] In some embodiments, the laser is a first laser configured for generating a first photon having a first wavelength; and the method further comprises irradiating the atomic vapor with a second laser configured for generating a second photon having a second wavelength.

[0016] In some embodiments, the method further comprises tuning the atomic vapor in the vacuum cell to a target frequency range by applying the voltage bias between the first electrode and the second electrode.

[0017] In some embodiments, the voltage bias is a direct current (DC) bias and exciting the atoms of the atomic vapor into the first Rydberg state is at least partially concurrent with applying the DC bias.

[0018] In some embodiments, the second electrode is a microchannel plate (MCP), the electron signal is an electrical current, and the method further comprises further comprising recording the electrical current based on the voltage bias across the MCP.

[0019] In some embodiments, the atomic vapor is contained within the vacuum cell.

[0020] In some embodiments, the atomic vapor is a beam of atoms. In some embodiments, the method further comprises: generating, with a collimated laser, the beam of atoms; transferring, with the collimated laser, the beam of atoms through the vacuum cell; and collecting, with a getter pump, the beam of atoms.

[0021] In some embodiments, the method further comprises: raising a temperature of the first electrode with a first electrode heating unit; raising a temperature of the second electrode with a second electrode heating unit, and by raising the temperatures of the first and second electrodes, removing ions and electrons from the first and second electrodes.

[0022] Also disclosed herein is an electrometer sensor for sensing an electromagnetic signal, the sensor comprising: a vacuum cell; an atomic vapor, wherein atoms of the atomic vapor are alkali atoms; a first electrode; a second electrode, wherein the atomic vapor is at least partially confined between the first electrode and the second electrode; a field control unit, comprising a first changeable voltage source electrically coupled with the first electrode and the second electrode, wherein the first changeable voltage source is configured for sweeping a voltage bias between the first electrode and the second electrode; an ion detector, comprising: a second changeable voltage source electrically coupled with the second electrode, wherein the second changeable voltage source is configured for applying the voltage bias across the second electrode; and an ammeter.

[0023] In some embodiments, the electrometer sensor, includes a user module, comprising a controller configured for: via the second changeable voltage source, applying the voltagebias between the first electrode and the second electrode; ionizing the atoms of the atomic vapor by sweeping the voltage bias between the first electrode and the second electrode via the first changeable voltage source; recording an electron signal at the second electrode, wherein the electron signal is representative of a population of atoms in at least one of the first Rydberg state and the second Rydberg state; and based on the electron signal, determining a strength of the electrical field of the electromagnetic signal.

[0024] In some embodiments, the electrometer sensor includes an ionization unit, comprising: a laser configured for: generating a photon; irradiating the atomic vapor within the vacuum cell; and by irradiating the atomic vapor, exciting the atoms of the atomic vapor into a first Rydberg state, wherein the controller is further configured for adjusting a wavelength of the photon.

[0025] In some embodiments, the voltage bias is a direct current (DC) bias and exciting the atoms of the atomic vapor into the first Rydberg state is at least partially concurrent with applying the DC bias.

[0026] In some embodiments, the second electrode is a microchannel plate (MCP), the electron signal is an electrical current, and the ammeter is configured to measure the electrical current.

[0027] In some embodiments, the laser is configured for generating a photon in an ultraviolet (UV) range.

[0028] In some embodiments, the laser is a first laser configured for generating a first photon having a first wavelength, and the electrometer sensor includes a second laser configured for generating a second photon having a second wavelength.

[0029] In some embodiments, the electromagnetic signal is characterized by an electrical field having a frequency between 300 GHz and 3 THz.

[0030] In some embodiments, the user module includes a readout device configured for recording the electrical current based on the voltage bias across the MCP over time.

[0031] In some embodiments, the atomic vapor is contained within the vacuum cell.

[0032] In some embodiments, the atomic vapor is a beam of atoms, and the electrometer sensor includes: a collimated laser configured for generating the beam of atoms andtransferring the beam of atoms through the vacuum cell; and a getter pump configured for collecting the beam of atoms,

[0033] In some embodiments, the electrometer sensor includes a first electrode heating unit configured for raising a temperature of the first electrode, as well as a second electrode heating unit configured for raising a temperature of the second electrode.BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0034] In order to describe the manner in which the above-recited issues can be addressed, a more particular description of the principles briefly described above will be rendered by reference to specific embodiments thereof that are illustrated in the appended drawings Understanding that these drawings depict only exemplary embodiments of the disclosure and are not therefore to be considered to be limiting of its scope, the principles herein are described and explained with additional specificity and detail through the use of the accompanying drawings in which:

[0035] FIG. 1 depicts a schematic diagram of an exemplary embodiment of an electrometer sensor configured for detecting an electromagnetic signal in accordance with the present technology.

[0036] FIG. 2A illustrates the process by which atomic vapor is excited by an ionization unit in accordance with the present technology

[0037] FIG. 2B illustrates the impact of a sensed electromagnetic signal on the excited atomic vapor in accordance with the present technology

[0038] FIG. 2C illustrates the impact of a voltage bias sweep on the atomic vapor and the process of state-selective field ionization (SFI) in accordance with one embodiment.

[0039] FIG. 3 depicts a block diagram of an exemplary embodiment of an electrometer sensor in accordance with the present technology.

[0040] FIG. 4 depicts a block diagram of an exemplary embodiment of an electrometer sensor in accordance with the present technology.

[0041] FIG. 5A and FIG. 5B illustrate a method 500 for sensing an electromagnetic signal based on changing states of atoms in an atomic vapor in accordance with the present technology.DETAILED DESCRIPTION

[0042] Various example embodiments of the disclosure are discussed in detail below. While specific implementations are discussed, it should be understood that this description is for illustration purposes only. A person skilled in the relevant art will recognize that other components and configurations may be used without parting from the spirit and scope of the disclosure. Thus, the following description and drawings are illustrative and are not to be construed as limiting Numerous specific details are described to provide a thorough understanding of the disclosure. However, in certain instances, well-known or conventional details are not described in order to avoid obscuring the description. References to one or an embodiment in the present disclosure can be references to the same embodiment or any embodiment; and, such references mean at least one of the example embodiments.

[0043] Reference to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosure. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative example embodiments mutually exclusive of other example embodiments. Moreover, various features are described which may be exhibited by some example embodiments and not by others. Any feature of one example can be integrated with or used with any other feature of any other example.

[0044] The terms used in this specification generally have their ordinary meanings in the art, within the context of the disclosure, and in the specific context where each term is used. Alternative language and synonyms may be used for any one or more of the terms discussed herein, and no special significance should be placed upon whether or not a term is elaborated or discussed herein. In some cases, synonyms for certain terms are provided. A recital of one or more synonyms does not exclude the use of other synonyms. The use of examples anywhere in this specification including examples of any terms discussed herein is illustrative only, and is not intended to further limit the scope and meaning of the disclosure or of any example term. Likewise, the disclosure is not limited to various example embodiments given in this specification.

[0045] Without intent to limit the scope of the disclosure, examples of instruments, apparatus, methods and their related results according to the example embodiments of thepresent disclosure are given below. Note that titles or subtitles may be used in the examples for convenience of a reader, which in no way should limit the scope of the disclosure.Unless otherwise defined, technical and scientific terms used herein have the meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. In the case of conflict, the present document, including definitions will control.

[0046] Additional features and advantages of the disclosure will be set forth in the description which follows, and in part will be obvious from the description, or can be learned by practice of the herein disclosed principles. The features and advantages of the disclosure can be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. These and other features of the disclosure will become more fully apparent from the following description and appended claims, or can be learned by the practice of the principles set forth herein.

[0047] For clarity of explanation, in some instances the present technology may be presented as including individual functional blocks representing devices, device components, steps or routines in a method embodied in software, or combinations of hardware and software.

[0048] In the drawings, some structural or method features may be shown in specific arrangements and / or orderings. However, it should be appreciated that such specific arrangements and / or orderings may not be required. Rather, in some embodiments, such features may be arranged in a different manner and / or order than shown in the illustrative figures. Additionally, the inclusion of a structural or method feature in a particular figure is not meant to imply that such feature is required in all embodiments and, in some embodiments, it may not be included or may be combined with other features.

[0049] While the concepts of the present disclosure are susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and will be described herein in detail. It should be understood, however, that there is no intent to limit the concepts of the present disclosure to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives consistent with the present disclosure and the appended claims.

[0050] FIG. 1 depicts a block diagram of an exemplary embodiment of an electrometer sensor 1000 configured for detecting an electromagnetic signal 130 in accordance with the present technology. Generally, the electrometer sensor 1000 may include a vacuum cell 100, a field control unit 110, an ionization unit 115, an ion detector 120, and a user module 125.

[0051] In some embodiments, a first electrode 105 and a second electrode are disposed within the vacuum cell 100. In some embodiments, the second electrode is a microchannel plate 106, as depicted in the illustrated embodiment. In some embodiments, an atomic vapor 101 may be contained within the vacuum cell 100; however, in additional embodiments, the atomic vapor 101 may be transferred through the vacuum cell 100 as a beam of atoms (see FIG. 3). In some embodiments, the atomic vapor 101 is comprised of alkali metal atoms. Examples of alkali metals that may comprise the atomic vapor 101 include rubidium (Rb), as depicted in the exemplary embodiment, as well as lithium (Li), sodium (Na), potassium (K), cesium (Cs), and francium (Fr). In some embodiments, the atomic vapor 101 is, in operation, at least partially confined between the first electrode 105 and the second electrode 106. In some embodiments, the vacuum cell 100 is configured for transitioning the atoms of the atomic vapor from a first Rydberg state to a second Rydberg state by a sensed electromagnetic signal 130. The sensed electromagnetic signal 130 may be characterized by an electrical field having a frequency between 300 GHz and 3 THz. In many embodiments, the sensed electromagnetic signal 130 is the signal that is present in the environment, and that is the object of the inventive measurement technology. Stated differently, a desired outcome of the measurements is a determination of the properties of the sensed electromagnetic signal 130, e.g., frequency, strength, periodic presence or absence, etc.

[0052] The field control unit 110 may include a first changeable voltage source 111 that is electrically coupled with the first electrode 105 and the microchannel plate 106. In some embodiments, the changeable voltage source Ill is configured to sweep a voltage bias between the first electrode 105 and the microchannel plate 106 (also referred to as the second electrode).

[0053] The ionization unit 115 may include a laser 116 that is configured to generate a photon 118 of an adjustable wavelength. The photon 118 may, in turn, irradiate the atomic vapor 101 within the vacuum cell 100, thereby exciting the atoms of the atomic vapor into the first Rydberg state. In some embodiments, the laser 116 emits photon 118 at anultraviolet range, which is sufficient to excite electrons 104 to the first Rydberg state. The ionization unit 115 may include a second laser 117 configured to generate a photon 119 of an adjustable wavelength. In some embodiments, the photon generated by the second laser 117 is different than the wavelength of the photon generated by the first laser 116. In some embodiments, the photon 118 emitted by the first laser 116 excites the atoms of the atomic vapor 101 to a higher orbital, while the photon 119 emitted by the second laser 117 excite the atoms of the atomic vapor 101 from the higher orbital to the first Rydberg state.

[0054] The ion detector 120 may include a second changeable voltage source 121 and an ammeter 122. In some embodiments, the changeable voltage source 121 is electrically coupled to the second electrode (microchannel plate 106 in the illustrated embodiment) and configured to generate a voltage bias across the microchannel plate 106. The voltage bias may be a direct current (DC) bias (also referred to as a “DC bias field”) between 1 kV and 2 kV. In some embodiments, the voltage bias is applied at least partially concurrently with the laser 116 irradiating and exciting the atoms of the atomic vapor 101 into the first Rydberg state. In some embodiments, the ammeter 122 is configured to measure an electrical current generated across the microchannel plate 106.

[0055] The user module 125 may include a controller 126. In some embodiments, the controller is configured for adjusting the wavelengths of the photons 118, 119 generated by the one or more lasers 116, 117. In some embodiments, the controller 126 is configured to apply a voltage bias across the first electrode, across the second electrode (microchannel plate 106), or between the two, using one or both of the changeable voltage source 111 and the changeable voltage source 121. The controller 126 may also be configured to sweep the voltage bias between the between the first electrode 105 and the microchannel plate 106 using one or both of the changeable voltage source 111 and the changeable voltage source 121, thereby ionizing the atoms of the atomic vapor 101. In some embodiments, the controller 126 is configured to record an electron signal at the microchannel plate 106, where the electron signal is representative of a population of atoms in at least one of the first Rydberg state and the second Rydberg state. Based on the electron signal, the controller 126 may be configured to determine a strength of the electric field of the sensed electromagnetic signal 130. The user module 125 may also include a readout device 127configured to record and display the electrical current based on the voltage bias across the microchannel plate 106 over time.

[0056] FIG. 2A, FIG. 2B, and FIG. 2C depict the physical interactions between atoms in the atomic vapor and other elements of the electrometer sensor according to the disclosed measurement sequence in accordance with the present technology In some embodiments, each measurement sequence consists of three steps.

[0057] FIG. 2A illustrates the process by which atomic vapor is excited by an ionization unit in accordance with the present technology and the method further illustrated in FIG. 5 A. In some embodiments, such as the embodiments illustrated in FIG. 1 and FIG. 2A, a first laser 116 emits a first photon 118 having a first wavelength, and a second laser 117 emits a second photon 119 having a second wavelength, exciting the atoms of the atomic vapor 101. Such embodiments constitute a two-photon transition. For example, the first laser 116 may emit a photon 118 having a wavelength of 780 nm, while the second laser 117 may emit a photon 119 having a wavelength of 480 nm. The excitation of the atoms by the first and second photons 118, 119 may excite the electrons 104 of the atoms to a first Rydberg state. According to the illustrated embodiment, the first photon 118 excites the electron 104 of a Rubidium atom from the 5S orbital to the 5P orbital, while the second photon 119 excites the electron 104 to the first Rydberg state nS. In some embodiments, the laser 116 emits a photon at an ultraviolet range, which is sufficient to excite the electron 104 to the first Rydberg state. This single-photon transition (not pictured) may relax laser stability requirements at the expense of the complexities of managing UV light.

[0058] In some embodiments, the excitation process lasts approximately 100 ns. The speed of the excitation process may be limited by available laser power and transition linewidth constraints from off-resonant excitation. In some embodiments, a DC bias field is applied across the microchannel plate during excitation, which may be a direct current (DC) bias between 1 kV and 2kV. In some embodiments, applying the DC bias field at least partially concurrently with laser excitation allows for the shifting of spectral lines of the excited atoms to desired first and, eventually, second Rydberg states, utilizing the Stark effect to tune the electrometer sensor to a desired detection frequency.

[0059] FIG. 2B illustrates the impact of a sensed electromagnetic signal 130 on the excited atomic vapor in accordance with the present technology.

[0060] In some embodiments, the electrometer sensor 1000 detects or receives an electromagnetic signal 130, which is characterized by an electrical field having a frequency between 300 GHz and 3 THz. As further explained below, the sensed electromagnetic signal 130 is the measured property whose strength is ultimately determined by the inventive technology. The electrical field may induce transitions of electrons 104 to adjacent Rydberg levels. The second Rydberg state may be near resonance with the electrical field of the electromagnetic signal 130 and have significant dipole matrix elements. According to the illustrated embodiment, the electron 104 transitions from a first Rydberg state nS to a second Rydberg state n'P. In some embodiments, both the first Rydberg state nS and the second Rydberg state n'P are near a determined ionization threshold related to the sensed electromagnetic signal (frequency between 300 GHz and 3 THz).

[0061] FIG. 2C illustrates the impact of a voltage bias sweep on the atomic vapor and the process of state-selective field ionization (SFI) in accordance with one embodiment.

[0062] In some embodiments, the controller 126 sweeps the voltage bias sweeps rapidly, ionizing the atoms of the atomic vapor 101 at distinct ionization thresholds. Referring to FIG. 1, this creates both free-floating, negatively charged electrons, as well as a positively charged rubidium ion 103. In some embodiments, the voltage bias sweeps (or “ramps”) between 0 and approximately 300 V / cm at a slew rate of approximately 0.5 V / cm / ns.

[0063] As the voltage bias sweeps, the positively charged rubidium ions 103 may be drawn to the negatively charged first electrode 105, while the electrons 104 may be drawn to the positively charged second electrode (microchannel plate 106 in FIG 1). In some embodiments, the quantity of the electrons 104 drawn to the microchannel plate 106 generate an electron signal that may be recorded by an ion detector 120. In some embodiments, the electron signal is an electrical current that is measured by an ammeter 122. The electron signal may be representative of a population of atoms in at least one of the first Rydberg state and the second Rydberg state. In some embodiments, the correlation between the applied voltage bias sweep and the time-dependent electron signal produces characteristic ionization spectral lines that encode the Rydberg level populations. By integrating the relative areas under these lines, THz-induced transition rates may be determined by a controller 126, enabling precise electric field measurements at frequenciesresonant with the Rydberg transition. The electron signal may then be recorded based on the voltage bias across the microchannel plate 106 and presented using a readout device 127

[0064] FIG. 3 and FIG. 4 depict block diagrams of exemplary embodiments of an electrometer sensor in accordance with the present technology. In some embodiments, it is necessary to prevent ion and electron accumulation on the electrode 105 and microchannel plate 106, respectively; however, there are multiple methods by which this may be accomplished.

[0065] In some embodiments, such as the exemplary embodiment illustrated in FIG. 3, the ionization unit 115 of an electrometer sensor 3000 includes a collimated laser 302 and a getter pump 303. In some embodiments, the collimated laser 302, by its operation, generates a beam of atoms 301 and transfers them through the vacuum cell 100, rather than utilizing a vacuum cell 100 that already contains an atomic vapor 101. Doing so may prevent the accumulation of rubidium ions 103 on the electrode 105 and electrons 104 on the microchannel plate 106, as they are no longer free floating in an atomic vapor 101 and instead follow a predictable path through the vacuum cell 100. In some embodiments, the beam of atoms 301 is collected by a getter pump 303. In some embodiments, the beam of atoms 301 may be energized by one or more lasers 116, 117 upon their entry into the vacuum cell 100 according to the process described in FIG. 2A. In some embodiments, the beam of atoms 301 is energized by the collimated laser 302 without the aid of additional lasers 116, 117.

[0066] In some embodiments, such as the exemplary embodiment illustrated in FIG. 4, the electrometer sensor 4000 includes one or more electrode heating units 401 that are electrically coupled with the first electrode 105 and the second electrode (microchannel plate 106). In some embodiments, the electrode heating units 401 raise the temperature of its coupled electrode 105, 106, raising the temperature of rubidium ions 103 and electrons 104 that are in contact with the electrodes 105, 106 and causing them to move to cooler parts of the vacuum cell. This may remove accumulated rubidium ions 103 and electrons 104 from the electrodes 105, 106, allowing for more accurate electron signal measurements In some embodiments, the electrodes are heated periodically between measurements; however, the controller 126 may be further configured to activate the electrode heating units 401 on demand if necessary. This allows for more instantaneous clearance of the electrodes 105,106, as opposed to the collimated laser approach illustrated in FIG 3, which is more continuous.

[0067] FIG. 5A and FIG. 5B illustrate a method 500 for sensing an electromagnetic signal based on changing states of atoms in an atomic vapor in accordance with the present technology. It should be understood that components identified in method 500 are analogous to components identified in the electrometer sensor 1000 discussed in FIG. 1; however other components may also be used In some embodiments, the method 500 may incorporate components identified in the electrometer sensor 3000 discussed in FIG. 3.

[0068] Throughout the following description of method 500, atoms to be energized within the electrometer sensor may be referred to as a beam of atoms or an atomic vapor, depending upon how the atoms enter the vacuum cell. It should be understood that the atoms will be referred to as a beam of atoms when they are generated outside of the vacuum cell, and an atomic vapor when they are previously disposed within the vacuum cell. It should also be understood that any steps concerning the atomic vapor may be applied to the beam of atoms as well. In some embodiments, a first electrode and a second electrode are disposed within the vacuum cell. In some embodiments, the second electrode is a microchannel plate, as depicted in FIG. 1, FIG. 3, and FIG. 4. In some embodiments, the atomic vapor 101 is at least partially confined between the first electrode and the second electrode.

[0069] In some embodiments, a beam of atoms may be generated outside of a vacuum cell 100. Beginning with optional step 502, a collimated laser may generate a beam of atoms. The beam of atoms may be comprised of an alkali metal. Examples of alkali metals that may comprise the beam of atoms include rubidium (Rb), as depicted in the exemplary embodiment, as well as lithium (Li), sodium (Na), potassium (K), cesium (Cs), and francium (Fr).

[0070] In optional step 504, the collimated laser may transfer the beam of atoms through the vacuum cell by emitting the beam of atoms.

[0071] In step 506, the atomic vapor is irradiated within the vacuum cell by at least one laser that is configured to generate a photon of an adjustable wavelength. In some embodiments, the laser is configured for generating a first photon having a first wavelengthand a second photon having a second wavelength. In some embodiments, the laser is configured for generating a photon in an ultraviolet (UV) range. The electrometer sensor may include a second laser configured to generate a photon of an adjustable wavelength. In some embodiments, the photon generated by the second laser is different than the wavelength of the photon generated by the first laser. In some embodiments, a controller is configured for adjusting the wavelengths of the photons generated by the one or more lasers.

[0072] In step 508, the photon may, in turn, excite the atoms of the atomic vapor into the first Rydberg state. The excitation of the atoms by the first and second photons may excite the electrons of the atoms to a first Rydberg state (referred to as a two-photon transition). In some embodiments, the laser emits a photon at an ultraviolet range, which is sufficient to excite the electrons to the first Rydberg state (referred to as a single-photon transition). In some embodiments, the excitation process lasts approximately 100 ns.

[0073] In step 510, a voltage bias may be applied by a changeable voltage source. In some embodiments, the voltage bias is applied at least partially concurrently with the laser 116 irradiating and exciting the atoms of the atomic vapor into the first Rydberg state. The voltage bias may be a direct current (DC) bias between 1 kV and 2 kV. In some embodiments, the controller may be configured for applying the voltage bias across the second electrode. In some embodiments, the controller may be configured for applying the voltage bias between the first electrode and the second electrode.

[0074] In step 512, exciting the atoms in the atomic vapor and applying the voltage bias at least partially concurrently may allow for the shifting of spectral lines of the excited atoms to desired first and, eventually, second Rydberg states, utilizing the Stark effect to tune the electrometer sensor to a desired detection frequency.

[0075] In step 514, the electrical field may induce transitions of electrons to adjacent Rydberg levels. The second Rydberg state may be near resonance with the electrical field of the electromagnetic signal and have significant dipole matrix elements. According to the illustrated embodiment, the electrons transitions from a first Rydberg state to a second Rydberg state. In some embodiments, both the first Rydberg state and the second Rydberg state are near a determined ionization threshold related to the sensed electromagnetic signal (frequency between 300 GHz and 3 THz).

[0076] In step 516, the voltage bias the controller may rapidly sweep the voltage bias with a changeable voltage source, ionizing the atoms at distinct ionization threshold. Referring to the exemplary embodiment in FIG. 1, this creates both an free-floating, negatively charged electrons, as well as a positively charged rubidium ions. In some embodiments, the voltage bias sweeps (or “ramps”) between 0 and approximately 300 V / cm at a slew rate of approximately 0.5 V / cm / ns. As the voltage bias sweeps, the positively charged rubidium ions may be drawn to the negatively charged first electrode, while the electrons may be drawn to the positively charged second electrode (microchannel plate in FIG. 1).

[0077] In optional step 518, the beam of atoms may be collected with a getter pump. In some embodiments, not all of the atoms in the beam of atoms are ionized to such an extent that the rubidium ions and the electrons may be drawn to their respective electrodes. Those that are not drawn to either electrode may be collected by the getter pump.

[0078] In step 520, the quantity of the electrons drawn to the microchannel plate may generate an electron signal. The electron signal may be representative of a population of atoms in at least one of the first Rydberg state and the second Rydberg state.

[0079] In step 522, the electron signal may be recorded by an ion detector. In some embodiments, the electron signal is an electrical current across the second electrode that is measured by an ammeter. The electron signal may then be recorded based on the voltage bias across the microchannel plate and presented using a readout device.

[0080] In step 524, the controller may determine a strength of the electrical field based on the electron signal. In some embodiments, the correlation between the applied voltage bias sweep and the time-dependent electron signal produces characteristic ionization spectral lines that encode the Rydberg level populations. By integrating the relative areas under these lines, THz-induced transition rates may be determined by a controller, enabling precise electric field measurements at frequencies resonant with the Rydberg transition. The strength of the electrical field may then be presented on a readout device.

[0081] The method 500 may then terminate, or proceed to the optional steps described in FIG. 5B.

[0082] In optional step 526, a first electrode heating unit may raise the temperature of the first electrode. In optional step 528, a second electrode heating unit may raise the temperature of the second electrode.

[0083] In optional step 530, raising the temperatures of the first and second electrodes may remove the ions and electrons from the first and second electrodes, respectively. In some embodiments, raising the temperature of the electrodes increases the temperature of the rubidium ions and electrons that are in contact with the electrodes, causing them to move to cooler parts of the vacuum cell. This may remove accumulated rubidium ions and electrons from the electrodes, allowing for more accurate electron signal measurements. In some embodiments, the electrodes are heated periodically between measurements; however, the controller may be further configured to activate the electrode heating units on demand if necessary.

[0084] The method 500 then terminates.

[0085] It should be understood that the above methods should be interpreted as merely representative. In some embodiments, process blocks may be performed simultaneously, sequentially, in a different order, or even omitted, without departing from the scope of this disclosure.

[0086] Throughout this specification, several terms of art are used. These terms are to take on their ordinary meaning in the art from which they come, unless specifically defined herein or the context of their use would clearly suggest otherwise. It should be noted that element names and symbols may be used interchangeably through this document (e.g., Si vs. silicon); however, both have identical meaning.

[0087] While illustrative embodiments have been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.

[0088] The present application may reference quantities and numbers. Unless specifically stated, such quantities and numbers are not to be considered restrictive, but representative of the possible quantities or numbers associated with the present application. Also, in this regard, the present application may use the term "plurality" to reference a quantity or number. In this regard, the term "plurality" is meant to be any number that is more than one,for example, two, three, four, five, etc. The terms "about," "approximately," "near," etc., mean plus or minus 5% of the stated value. For the purposes of the present disclosure, the phrase "at least one of A, B, and C," for example, means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C), including all further possible permutations when greater than three elements are listed.

[0089] Embodiments disclosed herein may utilize circuitry in order to implement technologies and methodologies described herein, operatively connect two or more components, generate information, determine operation conditions, control an appliance, device, or method, and / or the like. Circuitry of any type can be used. In an embodiment, circuitry includes, among other things, one or more computing devices such as a processor (e.g., a microprocessor), a central processing unit (CPU), a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or the like, or any combinations thereof, and can include discrete digital or analog circuit elements or electronics, or combinations thereof.

[0090] An embodiment includes one or more data stores that, for example, store instructions or data. Non-limiting examples of one or more data stores include volatile memory (e.g., Random Access memory (RAM), Dynamic Random Access memory (DRAM), or the like), non-volatile memory (e g., Read-Only memory' (ROM), Electrically Erasable Programmable Read-Only memory (EEPROM), Compact Disc Read-Only memory (CD-ROM), or the like), persistent memory, or the like. Further non-limiting examples of one or more data stores include Erasable Programmable Read-Only memory (EPROM), flash memory, or the like. The one or more data stores can be connected to, for example, one or more computing devices by one or more instructions, data, or power buses.

[0091] In an embodiment, circuitry includes a computer-readable media drive or memory slot configured to accept signal-bearing medium (e.g., computer-readable memory' media, computer-readable recording media, or the like). In an embodiment, a program for causing a system to execute any of the disclosed methods can be stored on, for example, a computer readable recording medium (CRMM), a signal-bearing medium, or the like. Non-limiting examples of signal-bearing media include a recordable type medium such as any form of flash memory, magnetic tape, floppy disk, a hard disk drive, a Compact Disc (CD), a Digital Video Disk (DVD), Blu-Ray Disc, a digital tape, a computer memory, or the like, as well astransmission type medium such as a digital and / or an analog communication medium (e g., a fiber optic cable, a waveguide, a wired communications link, a wireless communication link (e.g., transmitter, receiver, transceiver, transmission logic, reception logic, etc.). Further nonlimiting examples of signal-bearing media include, but are not limited to, DVD-ROM, DVDRAM, DVD+RW, DVD-RW, DVD-R, DVD+R, CD-ROM, Super Audio CD, CD-R, CD+R, CD+RW, CD-RW, Video Compact Discs, Super Video Discs, flash memory', magnetic tape, magneto-optic disk, MINIDISC, non-volatile memory card, EEPROM, optical disk, optical storage, RAM, ROM, system memory, web server, or the like.

[0092] The detailed description set forth above in connection with the appended drawings, where like numerals reference like elements, are intended as a description of various embodiments of the present disclosure and are not intended to represent the only- embodiments. Each embodiment described in this disclosure is provided merely as an example or illustration and should not be construed as preferred or advantageous over other embodiments. The illustrative examples provided herein are not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. Similarly, any steps described herein may be interchangeable with other steps, or combinations of steps, in order to achieve the same or substantially similar result. Generally, the embodiments disclosed herein are non¬ limiting, and the inventors contemplate that other embodiments within the scope of this disclosure may include structures and functionalities from more than one specific embodiment shown in the figures and described in the specification.

[0093] In the foregoing description, specific details are set forth to provide a thorough understanding of exemplary embodiments of the present disclosure. It will be apparent to one skilled in the art, however, that the embodiments disclosed herein may be practiced without embodying all the specific details. In some instances, well-known process steps have not been described in detail in order not to unnecessarily obscure various aspects of the present disclosure. Further, it will be appreciated that embodiments of the present disclosure may employ any combination of features described herein.

[0094] The present application may include references to directions, such as "vertical," "horizontal," "front," "rear," "left," "right," "top," and "bottom," etc. These references, and other similar references in the present application, are intended to assist in helping describeand understand the particular embodiment (such as when the embodiment is positioned for use) and are not intended to limit the present disclosure to these directions or locations

[0095] The principles, representative embodiments, and modes of operation of the present disclosure have been described in the foregoing description. However, aspects of the present disclosure, which are intended to be protected, are not to be construed as limited to the particular embodiments disclosed. Further, the embodiments described herein are to be regarded as illustrative rather than restrictive. It will be appreciated that variations and changes may be made by others, and equivalents employed, without departing from the spirit of the present disclosure. Accordingly, it is expressly intended that all such variations, changes, and equivalents fall within the spirit and scope of the present disclosure as claimed.

Claims

CLAIMSWhat is claimed is:

1. A method for sensing an electromagnetic signal based on changing states of atoms in an atomic vapor, the method comprising:irradiating the atomic vapor within a vacuum cell with a laser;by irradiating the atomic vapor, exciting the atoms of the atomic vapor into a first Rydberg state;applying a voltage bias between a first electrode and a second electrode, wherein the atomic vapor is at least partially confined between the first electrode and the second electrode;transitioning the atoms of the atomic vapor from the first Rydberg state to a second Rydberg state by the electromagnetic signal;ionizing the atoms of the atomic vapor by sweeping the voltage bias between the first electrode and the second electrode;by ionizing the atoms, generating an electron signal that is representative of a population of atoms in at least one of the first Rydberg state and the second Rydberg state;determining the electron signal at the second electrode by an ion detector; and based on the electron signal, determining a strength of the electrical field of the electromagnetic signal.

2. The method of claim 1,wherein the laser is a first laser configured for generating a first photon having a first wavelength; andwherein the method further comprises irradiating the atomic vapor with a second laser configured for generating a second photon having a second wavelength.

3. The method of claim 1, further comprising:by applying the voltage bias between the first electrode and the second electrode, tuning the atomic vapor in the vacuum cell to a target frequency range.

4. The method of claim 1,wherein the voltage bias is a direct current (DC) bias: andwherein exciting the atoms of the atomic vapor into the first Rydberg state is at least partially concurrent with applying the DC bias.

5. The method of claim 1,wherein the second electrode is a microchannel plate (MCP);wherein the electron signal is an electrical current; andwherein the method further comprises further comprising recording the electrical current based on the voltage bias across the MCP.

6. The method of claim 1, wherein the atomic vapor is contained within the vacuum cell.

7. The method of claim 1,wherein the atomic vapor is a beam of atoms;wherein the method further comprises:generating, with a collimated laser, the beam of atoms;transferring, with the collimated laser, the beam of atoms through the vacuum cell; andcollecting, with a getter pump, the beam of atoms.

8. The method of claim 1, wherein the method further comprises:raising a temperature of the first electrode with a first electrode heating unit; raising a temperature of the second electrode with a second electrode heating unit; andby raising the temperatures of the first and second electrodes, removing ions and electrons from the first and second electrodes.

9. An electrometer sensor for sensing an electromagnetic signal, the sensor comprising: a vacuum cell;an atomic vapor, wherein atoms of the atomic vapor are alkali atoms;a first electrode;a second electrode, wherein the atomic vapor is at least partially confined between the first electrode and the second electrode;a field control unit, comprising a first changeable voltage source electrically coupled with the first electrode and the second electrode, wherein the first changeable voltage source is configured for sweeping a voltage bias between the first electrode and the second electrode;an ion detector, comprising:a second changeable voltage source electrically coupled with the second electrode, wherein the second changeable voltage source is configured for applying the voltage bias across the second electrode; andan ammeter10. The electrometer sensor of claim 9, further comprising a user module, comprising:a controller configured for:via the second changeable voltage source, applying the voltage bias between the first electrode and the second electrode;ionizing the atoms of the atomic vapor by sweeping the voltage bias between the first electrode and the second electrode via the first changeable voltage source;recording an electron signal at the second electrode, wherein the electron signal is representative of a population of atoms in at least one of the first Rydberg state and the second Rydberg state; andbased on the electron signal, determining a strength of the electrical field of the electromagnetic signal.

11. The electrometer sensor of claim 10, further comprising:an ionization unit, comprising:a laser configured for:generating a photon;irradiating the atomic vapor within the vacuum cell; andby irradiating the atomic vapor, exciting the atoms of the atomic vapor into a first Rydberg state;wherein the controller is further configured for adjusting a wavelength of the photon.

12. The electrometer sensor of claim 10wherein the voltage bias is a direct current (DC) bias: andwherein exciting the atoms of the atomic vapor into the first Rydberg state is at least partially concurrent with applying the DC bias.

13. The electrometer sensor of claim 10,wherein the second electrode is a microchannel plate (MCP);wherein the electron signal is an electrical current; andwherein the ammeter is configured to measure the electrical current.

14. The electrometer sensor of claim 11, wherein the laser is configured for generating a photon in an ultraviolet (UV) range.

15. The electrometer sensor of claim 11,wherein the laser is a first laser configured for generating a first photon having a first wavelength; andwherein the electrometer sensor further comprises a second laser configured for generating a second photon having a second wavelength.

16. The electrometer sensor of claim 9, wherein the electromagnetic signal is characterized by an electrical field having a frequency between 300 GHz and 3 THz.

17. The electrometer sensor of claim 13, wherein the user module further comprises a readout device configured for recording the electrical current based on the voltage bias across the MCP over time,18. The electrometer sensor of claim 9, wherein the atomic vapor is contained within the vacuum cell.

19. The electrometer sensor of claim 9,wherein the atomic vapor is a beam of atoms;the electrometer sensor further comprising:a collimated laser configured for generating the beam of atoms and transferring the beam of atoms through the vacuum cell, anda getter pump configured for collecting the beam of atoms.

20. The electrometer sensor of claim 9, further comprising:a first electrode heating unit configured for raising a temperature of the first electrode; anda second electrode heating unit configured for raising a temperature of the second electrode.

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