Electromagnetic field detector

Abstract

The present invention provides an array of Rydberg atom-based electromagnetic field detectors comprising a plurality of Rydberg atom-based electromagnetic field detectors, where each Rydberg atom-based electromagnetic field detector is divided into a plurality of cells, each cell of the plurality of cells being: a variable transparency cell, a transparent film configured to change its transparency by electromagnetically inducing a transparency EIT effect, and further change its transparency in response to an incident electromagnetic field; the sequence of one or more variable transparency cells and one or more separator cells of the plurality of cells for the Rydberg atom-based electromagnetic field detector uniquely identifies the Rydberg atom-based electromagnetic field detector in the array of Rydberg atom-based electromagnetic field detectors.

Description

Technical Field

[0001] The present invention relates to an electromagnetic field detector based on Rydberg atoms. Background Art

[0002] Rydberg atoms are atoms that have one or more electrons excited to very high principal quantum numbers (e.g., >10). These Rydberg atoms have several useful properties, such as very large dipole moments and long decay periods.

[0003] Rydberg atoms can be used to detect electromagnetic fields. An electromagnetic field detector based on Rydberg atoms is based on the Electromagnetically Induced Transparency (EIT) effect. When a probe laser and a coupling laser are used to excite electrons in an atomic medium to a Rydberg state (i.e., an elevated energy state) through a sequential coherent excitation process, the EIT effect may be experienced. An excitation process called the ladder scheme uses the probe laser and the coupling laser to couple three different energy states: the probe laser resonantly couples the first state and the second state, and the coupling laser resonantly couples the second state and the third (Rydberg) state. In this third (Rydberg) state, the atomic medium becomes more transparent (i.e., absorbs less) to the probe laser because the first state and the second state are depleted and the third (Rydberg) state is populated. Then, a time-varying electromagnetic field incident on the atomic medium may cause a time-varying distortion of the energy level structure of the atomic medium. A specific third (Rydberg) state can be selected (by using the corresponding frequencies of the probe laser and the coupling laser) such that when a distortion of the energy level structure occurs due to the presence of the electromagnetic field, the coupling laser becomes non-resonant with the transition between the second state and the third (Rydberg) state in the distorted energy level structure. This limits the coupling between the second state and the third (Rydberg) state, and thus the atomic medium becomes less transparent (i.e., absorbs more) to the probe laser. Therefore, the electromagnetic field can be detected as a change in the intensity of the probe laser based on this change in transparency, resulting in an Amplitude Modulated (AM) electromagnetic field detector based on Rydberg atoms.

[0004] In other words, the frequencies of the probe laser and the coupling laser can be selected to couple the first state, the second state, and the third (Rydberg) state, where the energy difference between the third (Rydberg) state and the fourth (Rydberg) state corresponds to the energy of the electromagnetic field incident on the atomic medium. A more detailed explanation of this effect can be found in the article “A Multiple-Band Rydberg-Atom Based Receiver / Antenna: AM / FM Stereo Reception” by Holloway et al.

[0005] A Rydberg atom-based electromagnetic field detector can also be used to locate the source of an electromagnetic field. UK Patent Publication No. 2588754, which is incorporated herein by reference, discloses an optical fiber array that includes alternating sections of single-mode fiber (SMF) and hollow core fiber (HCF). Each HCF section includes an atomic medium excited to a specific Rydberg state and is thus configured to detect an electromagnetic field at a specific frequency. Each HCF section has a unique combination of separation distances to other HCF sections of the array. When an electromagnetic field passes through each HCF section of the array, the electromagnetic field causes a change in the transparency of the probe signal passing through that HCF section at that time. Since the attenuation of the probe signal caused by the electromagnetic field is proportional to the signal intensity when the electromagnetic field passes through the HCF section, and the signal intensity of the electromagnetic field is inversely proportional to the square of the distance traveled by the electromagnetic field, the attenuation of the probe signal in the HCF section closer to the source of the electromagnetic field will be greater compared to the attenuation of the probe signal in the HCF section farther from the source of the electromagnetic field. After the probe signal passes through the HCF sections in the array, the probe signal can be analyzed to determine the location of the source of the electromagnetic field based on the time difference between the change in transparency of the probe signal and the unique combination of separation distances of each HCF section to other HCF sections of the array. Summary of the Invention

[0006] According to a first aspect of the present invention, there is provided an array of Rydberg atom-based electromagnetic field detectors, which includes a plurality of Rydberg atom-based electromagnetic field detectors. Wherein, each Rydberg atom-based electromagnetic field detector is divided into a plurality of units, and each unit of the plurality of units is: a variable transparency unit, which is configured to change its transparency through the electromagnetically induced transparency (EIT) effect and further change its transparency in response to an incident electromagnetic field; or a separator unit, wherein a sequence of one or more variable transparency units and one or more separator units among the plurality of units for the Rydberg atom-based electromagnetic field detector uniquely identifies the Rydberg atom-based electromagnetic field detector in the array of Rydberg atom-based electromagnetic field detectors.

[0007] According to a second aspect of the present invention, there is provided an electromagnetic field detector, comprising: a light emitter; a light receiver; and an array of Rydberg atom-based electromagnetic field detectors according to the first aspect of the present invention, wherein: the light emitter is configured to: emit a probe signal to the light receiver at a probe frequency via the array of Rydberg atom-based electromagnetic field detectors, and emit a coupling signal to the light receiver at a coupling frequency via the array of Rydberg atom-based electromagnetic field detectors, wherein the probe frequency and the coupling frequency are set to change the transparency of the probe signal at each variable transparency unit of each Rydberg atom-based electromagnetic field detector in the array of Rydberg atom-based electromagnetic field detectors through an electromagnetically induced transparency (EIT) effect, and such that an electromagnetic field incident at the variable transparency unit of the Rydberg atom-based electromagnetic field detector in the array of Rydberg atom-based electromagnetic field detectors further changes the transparency of the probe signal at the variable transparency unit, so as to cause a detectable change in the power of the probe signal at the light receiver.

[0008] According to a third aspect of the present invention, there is provided a method of operating an electromagnetic field detector, the electromagnetic field detector comprising an array of Rydberg atom-based electromagnetic field detectors according to the first aspect of the present invention, the method comprising the steps of: monitoring a probe signal, wherein the probe signal and the coupling signal have been respectively emitted along the array of Rydberg atom-based electromagnetic field detectors at a probe frequency and a coupling frequency. Wherein the probe frequency and the coupling frequency are set to change the transparency of the probe signal at each variable transparency unit of each Rydberg atom-based electromagnetic field detector in the array of Rydberg atom-based electromagnetic field detectors through an electromagnetically induced transparency (EIT) effect, and such that an electromagnetic field incident at the variable transparency unit of the Rydberg atom-based electromagnetic field detector in the array of Rydberg atom-based electromagnetic field detectors further changes the transparency of the probe signal at the variable transparency unit, so as to cause a detectable change in the power of the probe signal at the light receiver; detecting an attenuation event as a sequence of one or more portions of the probe signal at a first power level and one or more portions of the probe signal at a second power level; and identifying a Rydberg atom-based electromagnetic field detector in the array of Rydberg atom-based electromagnetic field detectors by correlating the sequence of one or more portions of the probe signal at the first power level and one or more portions of the probe signal at the second power level of the detected attenuation event with a unique sequence for one or more variable transparency units and one or more separator units of a plurality of units of the Rydberg atom-based electromagnetic field detector.

[0009] The method may further include the following steps: identifying a plurality of Rydberg-atom-based electromagnetic field detectors in an array of Rydberg-atom-based electromagnetic field detectors, wherein at least one of the plurality of Rydberg-atom-based electromagnetic field detectors is identified by correlating a sequence of one or more probe signal portions at a first power level and one or more probe signal portions at a second power level of detected attenuation events with a unique sequence of one or more variable transparency units and one or more separator units of a plurality of units of the Rydberg-atom-based electromagnetic field detector; and determining the position of an emitter of an electromagnetic field based on the identified plurality of Rydberg-atom-based electromagnetic field detectors.

[0010] The method may further include the following steps: determining the distance between each of the identified plurality of Rydberg-atom-based electromagnetic field detectors and the emitter of the electromagnetic field, wherein the position of the emitter of the electromagnetic field is based on the determined distances between each of the identified plurality of Rydberg-atom-based electromagnetic field detectors and the emitter of the electromagnetic field. The step of determining the position of the emitter may be based on machine learning techniques.

[0011] According to a fourth aspect of the present invention, there is provided a computer program comprising instructions which, when executed by the electromagnetic field detector of the second aspect of the present invention, cause the electromagnetic field detector to perform the steps of the method of the third aspect of the present invention. The computer program may be stored on a computer-readable carrier medium.

[0012] A first subset of the variable transparency units in the plurality of units of the Rydberg-atom-based electromagnetic field detector among the plurality of Rydberg-atom-based electromagnetic field detectors may be configured to further change its transparency by a first amplitude in response to an incident electromagnetic field, and a second subset of the variable transparency units in the plurality of units of the Rydberg-atom-based electromagnetic field detector among the plurality of Rydberg-atom-based electromagnetic field detectors may be configured to further change its transparency by a second amplitude in response to an incident electromagnetic field.

[0013] The variable transparency unit may include a metal vapor, the metal vapor may be an alkali metal, and the alkali metal vapor may be one of the following: rubidium, cesium or strontium.

[0014] The electromagnetic field may be a radio frequency (RF) field. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to better understand the present invention, embodiments thereof will now be described by way of example only with reference to the accompanying drawings, in which:

[0016] Figure 1 is a schematic diagram of a cellular telecommunications network;

[0017] Figure 2Schematic diagram of a radio frequency (RF) detector array based on Rydberg atoms;

[0018] Figure 3 Schematic diagram of an RF detector array based on Rydberg atoms, an optical device housing, and a user equipment (UE);

[0019] Figure 4 Flowchart showing a method;

[0020] Figures 5a to 5c Schematic diagram showing RF pulses affecting three Rydberg atom-based RF detectors in a Rydberg atom-based RF detector array at a first moment, a second moment, and a third moment respectively;

[0021] Figure 5d Shows in Figures 5a to 5c Graph of the ratio of the received power to the transmitted power of the detection signal of the affected Rydberg atom-based RF detector array in the scenario of;

[0022] Figure 6 Graph showing the ratio of the received power to the transmitted power of the detection signal of a Rydberg atom-based RF detector array; and

[0023] Figure 7 Flowchart showing a method. Detailed implementation

[0024] In wireless telecommunications, wireless signals are transmitted at a specific power level, and their signal strength decreases with distance from the transmitter based on the path loss of the transmission environment. Once the signal strength of a wireless signal is no longer detectable above the background noise level at the detector, the wireless signal cannot be detected. The signal strength of the wireless signal at the detector is affected by other factors such as multipath propagation (due to reflection and refraction), dispersion, Doppler shadowing, and variable shadowing. Therefore, a wireless signal has a maximum range defined by its transmitted power, channel gain (which is a function of path loss and other factors), and background noise level.

[0025] In a cellular telecommunications network, wireless signals are transmitted between a base station and a user equipment (UE). Figure 1An example cellular telecommunications network is shown, which shows a base station and a UE and their respective coverage areas. In this scenario, the UE cannot receive a wireless signal from the base station and, without an alternative, cannot receive voice or data services. Additionally, since the base station is outside the coverage area of the UE, it cannot receive a wireless signal from the UE. Those skilled in the art will understand that this problem is experienced in other forms of wireless telecommunications, such as in a wireless local area network (WLAN), where two devices of the network cannot communicate because they are outside the respective coverage areas of the other device.

[0026] Figure 2 A Rydberg-atom-based radio frequency (RF) detector array 100 is shown. The Rydberg-atom-based RF detector array 100 includes an optical fiber having a plurality of Rydberg-atom-based RF detectors 120 located on the optical fiber. Each Rydberg-atom-based RF detector 120 is separated on the optical fiber from one or more of its adjacent Rydberg-atom-based RF detectors 120 by a single-mode fiber (SMF) section 130.

[0027] Figure 2 Also highlighted is the Rydberg-atom-based RF detector 120 of the array 100. The Rydberg-atom-based RF detector 120 includes a plurality of cells (indicated by tick marks on the axis), each cell having the same predetermined length and being an SMF cell 121 or a hollow-core fiber (HCF) cell 123. The Rydberg-atom-based RF detector 120 can include consecutive cells of the same type, as Figure 2 shown, where the second and third cells (from the left) of the highlighted Rydberg-atom-based RF detector 120 are both HCF cells. Each HCF cell 123 includes an optical cavity 125 that contains an alkali metal vapor (in this example, rubidium-85). The sequence of one or more HCF cells and one or more SMF cells in each Rydberg-atom-based RF detector 120 is unique to the Rydberg-atom-based RF detector 120 in the Rydberg-atom-based RF detector array 100. As described below, this sequence acts as a barcode to enable identification of a particular Rydberg-atom-based RF detector 120 associated with an attenuation event in a probe signal that has passed through the Rydberg-atom-based RF detector array 100.

[0028] In Figure 2 , the plurality of cells includes eight cells, but this is merely an example.

[0029] Figure 3 A first use case of the Rydberg-atom-based RF detector array 100 as a geolocator that is a wireless signal source in a wireless telecommunications network 1 is shown.Figure 3 Shown is an optical device housing 150 and a Rydberg-atom-based RF detector array 100 that originates from and terminates at the optical device housing 150. The position of each Rydberg-atom-based RF detector 120 of the array 100 is known. For example, these positions can be determined during a calibration phase, where global navigation satellite system (GNSS) coordinates are obtained at the position of each Rydberg-atom-based RF detector 120.

[0030] Figure 3 Also shown is a user equipment (UE) 140 as a wireless signal source having a specific frequency. In this example, the UE 140 is surrounded by the Rydberg-atom-based RF detector array 100.

[0031] The optical device housing 150 includes a probe laser 151, a coupling laser 153, a photodetector 155, and a non-reflective terminal 157. The probe laser 151 emits a probe signal along the Rydberg-atom-based RF detector array 100 in a first direction (e.g., clockwise), and the coupling laser 153 emits a coupling signal that counter-propagates and overlaps with the probe signal along the Rydberg-atom-based RF detector array 100 in a second direction (e.g., counterclockwise). The probe signal is directed towards the photodetector 155 after it passes through the Rydberg-atom-based RF detector array 100. The coupling signal is directed towards the non-reflective terminal 157 after it passes through the Rydberg-atom-based RF detector array 100.

[0032] In this embodiment, the probe signal resonates with the transition of the electrons of rubidium-85 atoms in each optical cavity of each HCF cell of each Rydberg-atom-based RF detector 120 in the Rydberg-atom-based RF detector array 100 from the ground state to the first excited state. Further, the coupling signal resonates with the transition of the electrons of rubidium-85 atoms in each optical cavity of each HCF cell of each Rydberg-atom-based RF detector 120 in the Rydberg-atom-based RF detector array 100 from the first excited state to a predetermined Rydberg state. In this configuration, each HCF cell of each Rydberg-atom-based RF detector 120 experiences the EIT effect, and the Rydberg-atom-based RF detector array 100 is more transparent to the probe signal (and can have low enough loss to be considered nearly transparent). Those skilled in the art will understand that in order to achieve the EIT effect along the entire length of the Rydberg-atom-based RF detector array 100, it is necessary to select the vapor density in the HCF cells, the number of HCF cells, and the power of the coupling laser such that the EIT effect is experienced in all HCF cells. That is, the coupling signal will be partially attenuated by each HCF cell in each Rydberg-atom-based RF detector 120, so the coupling laser must emit at a certain power such that (for a given number of HCF cells and a given density of vapor in the HCF cells) the coupling signal has sufficient power to cause the electrons in the final HCF cell to transition to the predetermined Rydberg state, thereby depopulating the ground state in the final HCF cell and making the final HCF cell more transparent to the probe signal.

[0033] The predetermined Rydberg state is selected based on the specific frequencies of the probe signal and the coupling signal such that the wireless signal (incident on one or more HCF cells 123) from the UE 140 has a frequency corresponding to the energy difference between the predetermined Rydberg state and another Rydberg state such that a change in the probe signal is detectable at the photodetector 155. In this example, where the UE 140 transmits a wireless signal at approximately 3.58891 GHz, the probe frequency is 780.2463 nm and the coupling frequency is 479.4370 nm such that the electrons are excited to the 84th Rydberg state.

[0034] Figure 4is a flowchart showing a first method. In a first step (S101) of this first method, a probe laser 151 and a coupling laser 153 respectively emit probe and coupling signals along a Rydberg-atom-based RF detector array 100 to excite each HCF cell of each Rydberg-atom-based RF detector 120 to a predetermined Rydberg state. In the absence of an incident RF field at the frequency to be detected, the probe signal will pass through the Rydberg-atom-based RF detector array 100 with minimal attenuation (because in the absence of an incident RF field, all HCF cells in the Rydberg-atom-based RF detector array 100 are more transparent to the probe signal), and is received at a photodetector 155. Since the travel time of the known probe signal has a very high accuracy, the received signal and the transmitted signal can be compared to determine the attenuation at each point of the probe signal. Assuming negligible transmission losses, the attenuation at each point of the probe signal is 0 dB, such that the ratio of the received power to the transmitted power of the probe signal is 100%.

[0035] In this example, the UE 140 emits an RF field in a single pulse (hereinafter referred to as an "RF pulse"). Thus, this RF pulse will pass through each HCF cell of each Rydberg-atom-based RF detector 120 of the Rydberg-atom-based RF detector array 100, and (as described above) will cause a change in the transparency of the probe signal passing through this HCF cell at this time. Since the attenuation of the probe signal caused by the RF pulse is proportional to the signal strength of the RF pulse when it passes through the HCF cell, and the signal strength of the RF pulse is a function of the channel gain, the attenuation of the probe signal of the HCF cell closer to the UE 140 will generally be greater than the attenuation of the probe signal of the HCF cell farther from the UE 140.

[0036] To illustrate these attenuations in more detail, Figures 5a to 5c illustrate the selection of three Rydberg-atom-based RF detectors (labeled A, B, and C) and the UE 140 in the Rydberg-atom-based RF detector array 100 at a first time instance, a second time instance, and a third time instance after the RF pulse is emitted from the UE 140. Figure 5d is a graph showing the ratio of the received power to the transmitted power of the probe signal received at the photodetector 155. The distance between the UE 140 and the Rydberg-atom-based RF detector B is less than the distance between the UE 140 and the Rydberg-atom-based RF detector 120A, which in turn is less than the distance between the UE 140 and the Rydberg-atom-based RF detector C. In addition, the distance between the Rydberg-atom-based RF detectors B and C is greater than the distance between the Rydberg-atom-based RF detectors A and B.

[0037] Figure 5aShows an RF pulse at a first time instance (as indicated by the dashed circle centered around UE 140), where the RF pulse passes through the nearest Rydberg-atom-based RF detector B but has not yet reached the Rydberg-atom-based RF detectors A and C. The RF pulse passes through the Rydberg-atom-based RF detector B, and during its passage causes the intensity of the probe signal passing through the Rydberg-atom-based RF detector B at this time to decay. Figure 5b Shows the RF pulse at a second time instance after the first time instance, where the RF pulse has propagated further from UE 140 such that it has passed beyond the Rydberg-atom-based RF detector B, is passing through the Rydberg-atom-based RF detector A, but has not yet reached the Rydberg-atom-based RF detector C. The RF pulse passes through the Rydberg-atom-based RF detector A, and during its passage causes the intensity of the probe signal passing through the Rydberg-atom-based RF detector A at this time to decay. Figure 5c Shows the RF pulse at a third time instance after the second time instance, where the RF pulse has propagated further from UE 140 such that it has passed beyond the Rydberg-atom-based RF detectors A and B and is now passing through the Rydberg-atom-based RF detector C. The RF pulse passes through the Rydberg-atom-based RF detector C, and during its passage causes the intensity of the probe signal passing through the Rydberg-atom-based RF detector C at this time to decay. Since the RF pulse is weaker during its passage through the Rydberg-atom-based RF detector C than during its passage through the Rydberg-atom-based RF detector A, and is weaker during its passage through the Rydberg-atom-based RF detector A than during its passage through the Rydberg-atom-based RF detector B (due to the relative distances and constant path loss), the attenuation of the probe signal passing through the Rydberg-atom-based RF detector B during the passage of the RF pulse is greater than the attenuation of the probe signal passing through the Rydberg-atom-based RF detector A during the passage of the RF pulse, and the attenuation of the probe signal passing through the Rydberg-atom-based RF detector A during the passage of the RF pulse is in turn greater than the attenuation of the probe signal passing through the Rydberg-atom-based RF detector C during the passage of the RF pulse. Figure 5dThe monitored signal at the photodetector 155 is shown, which shows the ratio of the received detection signal to the transmitted signal in order to indicate the attenuation intensity of the detection signal relative to time. The first attenuation received at the photodetector 155 is based on the attenuation of the Rydberg-atom-based RF detector C (which is closest to the photodetector 155), the second attenuation received at the photodetector 155 is based on the attenuation of the Rydberg-atom-based RF detector B, and the third attenuation received at the photodetector 155 is based on the attenuation of the Rydberg-atom-based RF detector A. Note that the time intervals between these attenuations are a combination of the time difference between the RF pulses arriving at the respective Rydberg-atom-based RF detectors and the time difference for the detection signal to pass through the Rydberg-atom-based RF detector array 100 between the respective Rydberg-atom-based RF detectors. Additionally, it should be noted that the time difference between the RF pulses arriving at the respective Rydberg-atom-based RF detectors causes the attenuation to appear further away or closer than the attenuation that would occur if the RF pulses passed through the Rydberg-atom-based RF detectors simultaneously, depending on whether the Rydberg-atom-based RF detector affected by the subsequent RF pulse is closer or further away from the photodetector than the Rydberg-atom-based RF detector affected by the previous RF pulse. In this example, when the Rydberg-atom-based RF detector A is further away from the photodetector 155, the attenuation of the detection signal of the Rydberg-atom-based RF detector A appears further away from the attenuation of the detection signal of the Rydberg-atom-based RF detector B (and thus, during the time period between the first time instance and the second time instance, the detection signal moves towards the photodetector 155 and away from the Rydberg-atom-based RF detector A), and when the Rydberg-atom-based RF detector C is closer to the photodetector 155, the attenuation of the detection signal of the Rydberg-atom-based RF detector C appears closer to the attenuation of the detection signal of the Rydberg-atom-based RF detector B (and thus, during the time period between the first time instance and the third time instance, the detection signal moves towards the photodetector 155 and towards the Rydberg-atom-based RF detector C).

[0038] On the scale of the Rydberg-atom-based RF detector array 100 (where different Rydberg-atom-based RF detectors 120 can have different respective distances to the source of the RF pulse), the attenuation experienced by each HCF cell of a particular Rydberg-atom-based RF receiver 120 can be different from the attenuation experienced by each HCF cell of different Rydberg-atom-based RF receivers 120. Additionally, as discussed above, these attenuations can be shifted (i.e., appear closer or further away than would occur if the RF pulses passed through the Rydberg-atom-based RF detectors simultaneously, as described above with respect to FIG. 5).

[0039] Since the size of each Rydberg-atom-based RF detector 120 in the array 100 is significantly smaller than the distance traveled by the RF pulse, it can be assumed that the signal strength experienced by each HCF unit of a particular Rydberg-atom-based RF detector 120 is equal (such that the attenuation caused by the RF pulse at each HCF unit of this Rydberg-atom-based RF detector 120 is the same). Nevertheless, for different HCF units of the Rydberg-atom-based RF detector 120, there may still be a shift in attenuation (as described above with respect to FIG. 5). This shift should not be the same as the predetermined length of the HCF unit 123 and the SMF unit 121 (e.g., equal to or greater than half of the predetermined length), which effectively sets the minimum length of the HCF unit 123 and the SMF unit 121 of the Rydberg-atom-based RF detector 120.

[0040] In step S103, the photodetector 155 monitors the probe signal after passing through the Rydberg-atom-based RF detector array 100. Figure 6 An example of the monitored probe signal is shown, which shows the attenuation events of each Rydberg-atom-based RF detector 120 of the array 100. Each attenuation event is a sequence of attenuations caused by the HCF unit of a particular Rydberg-atom-based RF detector 120. Due to the small distance between the HCF units relative to the large distance between the Rydberg-atom-based RF detectors 120, the attenuations in the attenuation sequence are closely spaced relative to the intervals between adjacent attenuation events.

[0041] In step S105, the identity of the Rydberg-atom-based RF detector 120 that causes each attenuation event in the monitored probe signal is determined. As described above, the multiple units of each Rydberg-atom-based RF detector 120 have a fixed predetermined length, which corresponds to a fixed duration in the monitored probe signal. Thus, each HCF unit of the Rydberg-atom-based RF detector 120 corresponds to the attenuation of the monitored probe signal within a fixed duration (and the number of consecutive HCF units of the Rydberg-atom-based RF detector 120 corresponds to the attenuation of the monitored probe signal within a time period equal to the number of HCF units multiplied by this fixed duration), and each SMF unit of the Rydberg-atom-based RF detector 120 corresponds to the probe signal at the reference level monitored within a fixed duration (and the number of consecutive SMF units of the Rydberg-atom-based RF detector 120 corresponds to the probe signal at the reference level monitored within a time period equal to the number of SMF units multiplied by this fixed duration).

[0042] Thus, the identity of the Rydberg-atom-based RF detector 120 that caused each attenuation event can be determined by identifying each portion of the probe signal at the first power level monitored over a fixed duration as an HCF cell and each portion of the probe signal at the second power level (i.e., the reference power level) monitored over a fixed duration as an SMF cell. The sequence of one or more portions of the probe signal at the first power level and one or more portions of the probe signal at the reference power level during an attenuation event corresponds to the sequence of one or more HCF cells and one or more SMF cells in the Rydberg-atom-based RF detector 120. Since this sequence is unique, the photodetector 155 can identify the Rydberg-atom-based RF detector 120 by matching the sequence of one or more portions of the probe signal at the first power level and one or more portions of the probe signal at the second power level in the determined attenuation event with a reference table (stored locally at the photodetector 155 or accessible via a communication interface) that stores the unique sequence of one or more HCF cells and one or more SMF cells in each Rydberg-atom-based RF detector 120.

[0043] The unique sequences of the HCF cells and SMF cells of all the Rydberg-atom-based RF detectors 120 in the array can include a specific subsequence. This enables the photodetector 155 to distinguish adjacent Rydberg-atom-based RF detectors 120 based on the presence of the subsequence in the sequence of the HCF cells and SMF cells after a period corresponding to the minimum distance between adjacent Rydberg-atom-based RF detectors 120 on the array 100. The subsequence can be placed at a specific relative position in the sequence, such as the start of the sequence. The subsequence can be, for example, a single HCF cell.

[0044] The reference table can also indicate the relative positions of each Rydberg-atom-based RF detector 120 in the array 100, such that only the identity of a single Rydberg-atom-based RF detector 120 needs to be identified as the cause of a particular attenuation event through the process outlined above, and the identities of the Rydberg-atom-based RF detectors 120 that caused each other attenuation event can be inferred from the relative positions.

[0045] In step S107, the distance between the Rydberg-atom-based RF detector 120 and the UE 140 is calculated for a plurality of Rydberg-atom-based RF detectors 120 as:

[0046]

[0047] where,

[0048] D Nis the distance between the Rydberg atom-based RF detector 120N and the UE 140,

[0049] AT N is the time at which the RF pulse (transmitted by the UE 140) attenuates the first Rydberg atom-based RF detector 120N,

[0050] AT M is the time at which the RF pulse attenuates the second Rydberg atom-based RF detector 120M.

[0051] T M，N is the time difference for the optical pulse to propagate between the first Rydberg atom-based RF detector 120N and the second Rydberg atom-based RF detector 120M,

[0052] A M is the amplitude of the attenuation event associated with the second Rydberg atom-based RF detector 120M.

[0053] A N is the amplitude of the attenuation event associated with the first Rydberg atom-based RF detector 120N.

[0054] The above equations are derived from the following analysis. It is known that the RF pulse travels between the UE 140 and the first Rydberg atom-based RF detector 120N at the speed of light in free space:

[0055]

[0056] where, RFT N is the arrival time of the RF pulse at the first Rydberg atom-based RF detector 120N.

[0057] It is also assumed that there is a constant path loss for the RF pulse between the UE 140 and the first Rydberg atom-based RF detector 120N:

[0058]

[0059] where, P is a constant and is assumed to be equal for all Rydberg atom-based RF detectors 120.

[0060] The time difference between the reception time of the attenuation event at the second Rydberg atom-based RF detector 120M and the reception time of the attenuation event at the first Rydberg atom-based RF detector 120N can be expressed as:

[0061] AT M -AT N =T M，N +RFT M -RFT N(3)

[0062] Rearranging equations (1) to (3), and assuming that the constant P is constant in all HCF sections, the following solutions can be derived:

[0063]

[0064] In step S109, using known multi-point positioning techniques, the position of UE 140 is determined based on the distances between UE 140 and a number of Rydberg atom-based RF detectors 120 and the position of each of those Rydberg atom-based RF detectors.

[0065] The above-described Rydberg atom-based RF detector array 100 and method are improved methods for geolocating wireless signal sources. The Rydberg atom-based RF detectors of UK Patent Publication No. 2588754 require a specific separation distance from other HCF cells of the detector. In contrast, the position of each Rydberg atom-based RF detector 120 on the Rydberg atom-based RF detector array 100 is independent of the position of any other Rydberg atom-based RF detector 120 on the array 100. This independence improves the flexibility of the device, such that an increased density of Rydberg atom-based RF detectors 120 can be achieved by using relatively short distances between a first subset of Rydberg atom-based RF detectors on one part of the array 100 relative to a second subset of Rydberg atom-based RF detectors on the array 100. Since each Rydberg atom-based RF detector 120 can also operate as a receiver (where the RF signal received at the Rydberg atom-based RF detector 120 is demodulated), this increased density of Rydberg atom-based RF detectors 120 can be used in areas of a wireless network that increase the demand for uplink capacity. Additionally, this independence allows additional Rydberg atom-based RF detectors 120 to be added to the array 100 after the array is deployed.

[0066] The density of the Rydberg atom-based RF detectors 120 can also be increased by deploying the array 100 such that a first subset of Rydberg atom-based RF detectors 120 in one part of the array 100 are spaced closely to each other relative to a second subset of detectors 120 of the array 100, such as by winding or zigzagging the part of the array 100 that includes the first subset of Rydberg atom-based RF detectors 120.

[0067] In the above embodiments, the function indicated in step S107 above is used to calculate the distance between the Rydberg-atom-based RF detector 120 and the UE 140 for a plurality of Rydberg-atom-based RF detectors 120, and then in step S109, multilateration techniques are used to determine the location of the UE 140. However, those skilled in the art will understand that other methods of geolocating the UE 140 based on the monitored probe signals are possible. For example, machine learning methods can be used. The machine learning method can implement a training phase to determine the geolocation function. The training phase can be based on training data, where a set of input parameters (including one or more of the following: the monitored probe signal, the identity of the Rydberg-atom-based RF detector 120 that causes each attenuation event in the monitored probe signal, and the location of each Rydberg-atom-based RF detector 120 (e.g., GNSS coordinates)) are mapped to an output parameter (the location of the UE 140) through supervised learning. The training data can be obtained by transmitting RF pulses from the UE 140 at multiple locations and recording each location (e.g., its GNSS coordinates) and its corresponding monitored probe signal. As described above, when the array 100 is deployed, the location of each Rydberg-atom-based RF detector 120 can be recorded. The known location of the UE 140 can involve the known path of the UE 140 (e.g., a series of locations) and its corresponding series of monitored probe signals.

[0068] Once the geolocation function has been determined after the training phase (and optionally a validation phase using validation data), it can be used to determine the location of the source of the RF pulse after identifying the Rydberg-atom-based RF detector 120 that causes each attenuation event in the monitored probe signal (in step S105 above). A retraining phase can be implemented (e.g., periodically or in response to known changes in the propagation environment) to update the geolocation function.

[0069] Steps S107 and S109 above are particularly suitable for geolocating the UE 140 when the attenuation of the signal strength of the RF pulse is mainly due to path loss relative to the above additional factors such as multipath propagation (due to reflection and refraction), dispersion, Doppler shadowing, and variable shadowing. The machine learning method discussed above is suitable for geolocating the UE 140 regardless of the cause of the signal strength attenuation.

[0070] Those skilled in the art will understand that the unique sequence of the HCF unit and the SMF unit of each Rydberg-atom-based RF detector 120 can be implemented with any number of units as long as the number of unique combinations is equal to or greater than the number of Rydberg-atom-based RF detectors 120 in the array 100.

[0071] In the above embodiments, the HCF section includes an atomic medium based on rubidium-85 that may experience the EIT effect and has Rydberg states, where the Rydberg states have an energy difference related to the photon energy of the frequencies used in radio communication protocols. Thus, the RF detector can be configured to detect RF waves of a specific frequency by setting the probe frequency and the coupling frequency to excite electrons to a specific Rydberg state, where the energy difference between this Rydberg state and the next Rydberg state matches the photon energy of the RF wave to be detected. Thus, those skilled in the art will understand that the use of rubidium-85 is not essential, and any atomic medium that can respond to RF waves so as to change its transparency to the probe signal can be used in the above embodiments. Thus, the RF detector does not need to be an end-to-end optical fiber, but can be any device having interleaved separator sections and an RF detector section based on Rydberg atoms. Further, it is not essential that the optical fiber sections between the RF detector sections based on Rydberg atoms be made of SMF. For example, multimode optical fiber can be used alternatively. In another example, the sections between the RF detectors based on Rydberg atoms are also constructed of HCF, but with different concentrations of rubidium to ensure that the attenuation events caused by the HCF cells of the RF detectors based on Rydberg atoms can be distinguished in the probe signal.

[0072] Further, it is not essential that each RF detector 120 based on Rydberg atoms includes a specific subsequence such that the attenuation events caused by the RF detector 120 based on Rydberg atoms are distinguishable in the probe signal. As described above, the sections between the RF detectors 120 based on Rydberg atoms can be composed of HCF and are configured such that their response to the incident RF field can be distinguished from the responses of the HCF cells and SMF cells of the RF detectors 120 based on Rydberg atoms. Thus, the photodetector 155 can identify the start of each sequence of the HCF cells and SMF cells in each RF detector 120 based on the change in response with respect to the response of the HCF to the incident RF field between the RF detectors 120 based on Rydberg atoms.

[0073] It is also not essential that the detector be configured to detect an electromagnetic field in the RF band of the electromagnetic spectrum. That is, the detector can be configured such that the variable transparency section changes its transparency in response to an incident electromagnetic field in other parts of the spectrum (e.g., by using an atomic medium having specific energy states and by selecting appropriate probe frequencies and coupling frequencies, as described above). Thus, the method of the above embodiments can be used as an electromagnetic field detector. As described above, it is also not essential to use a ladder excitation scheme to experience the EIT effect. Other schemes, such as λ or Vee, can be used alternatively.

[0074] In addition, it is not necessary for the detection signal and the coupling signal to propagate in opposite directions. However, this is preferred because the Doppler shift effect can be ignored.

[0075] The above-described Rydberg atom-based RF detector array 100 generates a binary response at the photodetector 155, where each HCF cell corresponds to a detection signal at a first power level and each SMF cell corresponds to a detection signal at a reference power level. In another implementation, the HCF cells can be designed to cause different attenuations in the detection signal such that a first subset of the HCF cells of the Rydberg atom-based RF detector corresponds to a detection signal at a first power level and a second subset of the HCF cells of the Rydberg atom-based RF detector corresponds to a detection signal at a second power level. This can be achieved by using different concentrations of rubidium in the HCF cells. Then, a sequence of one or more SMF cells (corresponding to a detection signal at a reference power level), one or more HCF cells of the first subset of the HCF cells (corresponding to a detection signal at a first power level), and one or more HCF cells of the second subset of the HCF cells (corresponding to a detection signal at a second power level) can be used to uniquely identify the Rydberg atom-based RF detector. This further implementation increases the number of unique combinations of sequences available for identifying the Rydberg atom-based RF detector by operating as a two-dimensional barcode.

[0076] The above method illustrates a first use case of the Rydberg atom-based RF detector array 100 for geolocating an RF field source. However, those skilled in the art will understand that the Rydberg atom-based RF detector array 100 can be used to identify the Rydberg atom-based RF detectors 120 of the array 100 that detect an RF field.

[0077] The Rydberg-atom-based RF detector array 100 has additional benefits because the orientation of each Rydberg-atom-based RF detector 120 is a non-essential configuration. That is, since each HCF cell 123 of each Rydberg-atom-based RF detector 120 is relatively short, its orientation relative to the incident RF pulse has an insignificant effect on the attenuation of each HCF cell 123. Nevertheless, the orientation of each Rydberg-atom-based RF detector 120 can also be used as an input parameter for the training data used in the machine learning method described above. This orientation parameter can enable the geolocation function determined during the training phase to geolocate the UE 140 and determine the angle of arrival of the RF pulse at each Rydberg-atom-based RF detector 120. Therefore, the training data can also include the orientation of each Rydberg-atom-based RF detector 120 (obtained by a suitable orientation sensor during deployment or use) (as input data) and the angle of arrival of the RF pulse at each Rydberg-atom-based RF detector 120 (calculated based on the position of the UE 140 and the position of each Rydberg-atom-based RF detector 120) (as output data).

[0078] Figure 7 A method including the following steps is shown: (step S201) monitoring a probe signal, wherein the probe signal and a coupling signal have been respectively transmitted along the Rydberg-atom-based electromagnetic field detector array at a probe frequency and a coupling frequency, wherein the probe frequency and the coupling frequency are set to change the transparency of the probe signal at each variable transparency cell of each Rydberg-atom-based electromagnetic field detector in the Rydberg-atom-based electromagnetic field detector array through the electromagnetically induced transparency (EIT) effect, and enabling the electromagnetic field incident at the variable transparency cell of the Rydberg-atom-based electromagnetic field detector in the Rydberg-atom-based electromagnetic field detector array to further change the transparency of the probe signal at the variable transparency cell, so as to cause a detectable change in the power of the probe signal at the optical receiver; (step S203) detecting an attenuation event as a sequence of one or more probe signal portions at a first power level and one or more probe signal portions at a second power level; and (step S205) identifying the Rydberg-atom-based electromagnetic field detector in the Rydberg-atom-based electromagnetic field detector array by correlating the sequence of one or more probe signal portions at the first power level and one or more probe signal portions at the second power level of the detected attenuation event with a unique sequence of one or more variable transparency cells and one or more separator cells of the Rydberg-atom-based electromagnetic field detector.

[0079] Those skilled in the art will understand that any combination of features is possible within the scope of the claimed invention.

Claims

1. An array of electromagnetic field detectors based on Rydberg atoms, the array of electromagnetic field detectors based on Rydberg atoms comprising a plurality of electromagnetic field detectors based on Rydberg atoms, wherein, Each Rydberg-atom-based electromagnetic field detector is divided into a plurality of units, and each unit of the plurality of units is: a variable transparency unit configured to change the transparency of the variable transparency unit by an electromagnetically induced transparency (EIT) effect and further change the transparency of the variable transparency unit in response to an incident electromagnetic field, or a separator unit, wherein the Rydberg-atom-based electromagnetic field detector in the Rydberg-atom-based electromagnetic field detector array is uniquely identified by a sequence of one or more variable transparency units and one or more separator units of the plurality of units of the Rydberg-atom-based electromagnetic field detector.

2. The array of electromagnetic field detectors based on Rydberg atoms according to claim 1, wherein, A first subset of the variable transparency units of the plurality of units of the Rydberg-atom-based electromagnetic field detector among the plurality of Rydberg-atom-based electromagnetic field detectors is configured to further change the transparency of the first subset of the variable transparency units by a first amplitude in response to the incident electromagnetic field, and a second subset of the variable transparency units of the plurality of units of the Rydberg-atom-based electromagnetic field detector among the plurality of Rydberg-atom-based electromagnetic field detectors is configured to further change the transparency of the second subset of the variable transparency units by a second amplitude in response to the incident electromagnetic field.

3. The array of electromagnetic field detectors based on Rydberg atoms according to claim 1 or claim 2, wherein, The variable transparency unit includes a metal vapor.

4. The electromagnetic field detector based on Rydberg atoms according to claim 3, wherein, The metal vapor is an alkali metal.

5. The electromagnetic field detector based on Rydberg atoms according to claim 4, wherein, The alkali metal vapor is one of rubidium, cesium, or strontium.

6. The electromagnetic field detector based on Rydberg atoms according to any one of the preceding claims, wherein, The electromagnetic field is a radio frequency (RF) field.

7. An electromagnetic field detector, the electromagnetic field detector comprising: An optical transmitter; An optical receiver; and A Rydberg-atom-based electromagnetic field detector array according to any one of claims 1 to 6, wherein: The optical transmitter is configured to: emit an optical detection signal to the optical receiver at a detection frequency via the Rydberg-atom-based electromagnetic field detector array, and emit a coupling signal to the optical receiver at a coupling frequency via the Rydberg-atom-based electromagnetic field detector array, wherein the detection frequency and the coupling frequency are set to change the transparency of the detection signal at each variable transparency unit of each Rydberg-atom-based electromagnetic field detector in the Rydberg-atom-based electromagnetic field detector array by an electromagnetically induced transparency (EIT) effect, and such that the electromagnetic field incident on the variable transparency unit of the Rydberg-atom-based electromagnetic field detector in the Rydberg-atom-based electromagnetic field detector array further changes the transparency of the detection signal at the variable transparency unit, so as to cause a detectable change in the power of the detection signal at the optical receiver.

8. A method of operating an electromagnetic field detector, the electromagnetic field detector comprising an array of electromagnetic field detectors based on Rydberg atoms according to any one of claims 1 to 6, the method comprising the following steps: Monitor a detection signal, wherein the detection signal and a coupling signal are respectively transmitted along the Rydberg-atom-based electromagnetic field detector array at a detection frequency and a coupling frequency, wherein the detection frequency and the coupling frequency are set to change the transparency of the detection signal at each variable transparency unit of each Rydberg-atom-based electromagnetic field detector in the Rydberg-atom-based electromagnetic field detector array through an electromagnetically induced transparency (EIT) effect, and to further change the transparency of the detection signal at the variable transparency unit by an electromagnetic field incident on the variable transparency unit of the Rydberg-atom-based electromagnetic field detector in the Rydberg-atom-based electromagnetic field detector array, so as to cause a detectable change in the power of the detection signal at the optical receiver; Detect an attenuation event as a sequence of one or more detection signal portions at a first power level and one or more detection signal portions at a second power level; and Identify a Rydberg-atom-based electromagnetic field detector in the Rydberg-atom-based electromagnetic field detector array by correlating the sequence of one or more detection signal portions at the first power level and one or more detection signal portions at the second power level of the detected attenuation event with a unique sequence of one or more variable transparency units and one or more separator units among the plurality of units of the Rydberg-atom-based electromagnetic field detector.

9. The method according to claim 8, the method further comprising the following steps: Identify a plurality of Rydberg-atom-based electromagnetic field detectors in the Rydberg-atom-based electromagnetic field detector array, wherein at least one of the Rydberg-atom-based electromagnetic field detectors is identified by correlating the sequence of one or more detection signal portions at the first power level and one or more detection signal portions at the second power level of the detected attenuation event with a unique sequence of one or more variable transparency units and one or more separator units among the plurality of units of the Rydberg-atom-based electromagnetic field detector; and Determine the position of the emitter of the electromagnetic field based on the identified plurality of Rydberg-atom-based electromagnetic field detectors.

10. The method according to claim 9, the method further comprising the following steps: Determine the distance between each of the identified plurality of Rydberg-atom-based electromagnetic field detectors and the emitter of the electromagnetic field, wherein the position of the emitter of the electromagnetic field is based on the determined distances between each of the identified plurality of Rydberg-atom-based electromagnetic field detectors and the emitter of the electromagnetic field.

11. The method according to claim 9, wherein, The step of determining the position of the emitter is based on machine learning techniques.

12. A computer program, the computer program comprising instructions which, when the computer program is executed by the electromagnetic field detector according to claim 7, cause the electromagnetic field detector to perform the steps according to any one of claims 8 to 11.

13. A computer-readable carrier medium, the computer-readable carrier medium comprising the computer program according to claim 12.

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