Physicists Develop a New Type of Antenna
A team of University of Otago researchers and physicists have demonstrated a new form of antenna, developed with a small glass bulb containing an atomic vapor. The bulb was wired with laser beams and could therefore be placed far from any receiver electronics.
Dr. Susi Otto, from the Dodd-Walls Centre for Photonic and Quantum Technologies, led the field testing of the portable atomic radio frequency sensor. Such sensors, that are enabled by atoms in a so-called Rydberg state, can provide superior performance over current antenna technologies as they are highly sensitive, have broad tunability, and small physical size, making them attractive for use in defense and communications.
For example, they could simplify communications for soldiers on the battlefield as they cover the full spectrum of radio frequencies, rather than needing multiple antennas to cover different frequency bands, and are super sensitive and accurate to detect a wide range of critical signals. The ability to eliminate the need for multiple sensors also makes them useful in satellite technology.
Importantly, compared to more traditional sensors, Rydberg sensors can function without any metal parts, which can scatter the radio frequency field of interest and the atomic sensor is accessed via laser light, replacing the need for electric cables. The new design developed by the team of Otago physicists is portable and can be taken outside the laboratory. In a first out-of-lab demonstration, the sensor was able to efficiently measure fields in a distance of 30 meters using a freespace laser link, adding important flexibility to Rydberg-atom based sensing technologies.
The team detailed the development of the new sensor and its demonstration in a paper that was recently published in Applied Physics Letters.
Moving Beyond the Lab and Physical Constraints
In 2012, a seminal work by Sedlacek et al. demonstrated the use of Rydberg-excited 87Rb atoms in a glass vapor cell as a sensitive detector for microwave fields. In their scheme, the presence and strength of microwave radiation resonant with the transition between two Rydberg states were measured by sending counter-propagating blue and infrared laser beams through the vapor cell. In the absence of microwave radiation, the blue coupling light would establish electromagnetically induced transparency (EIT) for the infrared probe light, while an incoming microwave field of constant amplitude would split the EIT transmission peak into two, and from the peak separation of these two Autler–Townes (AT) peaks, the microwave field strength could be inferred. Because atomic transitions lie at the heart of this ingeniously simple experimental scheme, it offers SI traceable and calibration free electrometry. 2
The decade following the original work of Sedlacek1 et al. witnessed a number of developments. For example, the sensitivity of the on-resonant EIT/AT technique can be greatly improved using a superheterodyne receiver architecture and an optical ground-state repumping technique, making it possible to detect fields down to 5 μV m–1. In the other extreme, at large RF field strengths, the AT splitting is no longer linear with the strength of the applied field due to the AC Stark shift, which scales as the field strength squared. Instead, this shift can be measured to infer the field strengths of sufficiently large fields.
Measurements of the AC Stark shift also allow detection of frequencies outside the discrete set of atomic Rydberg transitions extending the technique to a continuous RF spectrum. Rydberg-atomic systems for communication constitute a particular application that leverages the technique of Sedlacek et al., and fundamental working principles of analog and digital communication have been demonstrated in a range of atom-based systems.
Although the systems mentioned above allow for a large variety of RF measurements and applications, they are almost invariably confined to an optical table in a laboratory due to the requirement to counter-align the two (or more) laser beams within the atomic vapor cell. The Otago team created a proof-of-concept setup capable of increased mobility, replacing the fiber access to the vapor cell with two freespace laser beams and a corner-cube prism reflector, which reflects the probe beam back to a photodetector. Without any significant effort, the portable atomic RF probe can be deployed to sense fields at a distance exceeding 30 m from the active components — the lasers and photodetector.
Figure 1 shows a schematic of the experimental setup, highlighting the base station and the separate portable transducer, in the following referred to as “sensing unit.” Also shown are the relevant atomic levels of 87Rb involved in the RF-to-optical transduction. The base station contains all the required elements to prepare two light fields for a two-photon Rydberg EIT system, i.e., a coupling and probe laser, their driver electronics, and a setup for the frequency stabilization of the two lasers. Specifically, the team employs a coupling laser with a wavelength of 480 nm and a maximum power of 10 mW. After passing through a beam expander, the coupling beam has a 1/ e2 beam diameter of ~ 6 mm corresponding to a Rayleigh length of about 60 m. For parts of the demonstration, the coupling laser is stabilized to a high-finesse cavity using the Pound–Drever–Hall technique, which results in a root-mean square (RMS) linewidth below 100 kHz.
The stand-alone sensing unit is optically linked to the base station via the two free space laser beams and only incorporates two elements: a 150 mm-long and 27 mm-wide cylindrical vapor cell containing a rubidium vapor at room temperature and a corner-cube prism reflector (Thorlabs PS975-A). The prism reflector allows us to accommodate two pairs of counter-propagating probe and coupling beams, passing through the vapor cell with minimal alignment effort.
When coupled to a Rydberg state via the optical two-photon transition, the rubidium atoms become sensitive to RF radiation. In particular, this happens for RF frequencies that couple the Rydberg level resonantly to other nearby Rydberg levels. For sufficiently large fields, the atoms are receptive to a broad range of RF signals via the AC Stark shift. In the demonstration, a home-built helical antenna broadcasts an amplitude modulated (AM) microwave signal with carrier frequencies between 16 and 20 GHz. The antenna radiates circularly polarized microwave fields along the axis of the helix. The AM signal is imprinted onto the probe light field via the atoms and is retrieved from the light field at the base station using a photo detector and a spectrum analyzer.
This research and demonstration presents a simple technique for a remote Rydberg-atom-based RF sensor, which was verified for distances of up to 30 m between the passive sensing unit and the base station — currently limited by the length of the hallway used in the demonstration. The researchers remark that their work shares challenges with remotely interrogated atomic magnetometers, which operate in a similar fashion to a Rydberg microwave detector. A free-space optical setup, as discussed in this work, is applicable to these systems, though a polarization-preserving retroreflector might be needed.
The researchers envision these developments eventually making quantum sensors more robust and cost-effective, enabling them to move out of labs and into the real world.
- J. Sedlacek, A. Schwettmann, H. Kübler, R. Löw, T. Pfau, and J. Shaffer, Nat. Phys. 8, 819 (2012). https://doi.org/10.1038/nphys2423
- C. L. Holloway, M. T. Simons, J. A. Gordon, A. Dienstfrey, D. A. Anderson, and G. Raithel, J. Appl. Phys. 121, 233106 (2017). https://doi.org/10.1063/1.4984201
Material for this article was provided by the University of Otago and part of the paper published by the team of physicists, in Applied Physics Letters. For more information, visit here .
Watafiti wa Chuo Kikuu cha Otago wameonyesha aina mpya ya antena, iliyoundwa na bulb ndogo ya kioo iliyo na mvuke wa atomu. Balbu hiyo ilikuwa na nyaya zenye miale ya laser na kwa hiyo ingeweza kuwekwa mbali na vifaa vyovyote vya elektroniki vya mpokeaji. Daktari Susi Otto, kutoka Kituo cha Dodd-Walls cha Teknolojia za Photonic na Quantum, aliongoza majaribio ya uwanja wa sensorer ya masafa ya redio ya atomiki inayoweza kubebwa. Sensorer hizo, ambazo zinaendeshwa na atomu katika hali inayoitwa Rydberg, zinaweza kutoa utendaji bora kuliko teknolojia za antena za sasa, kwani zina hisia nyingi, zina uwezo mkubwa wa kurekebisha, na ukubwa mdogo wa kimwili, na kuzifanya kuwa za kuvutia kwa matumizi katika ulinzi na mawasiliano. Kwa mfano, inaweza kurahisisha mawasiliano kwa askari katika uwanja wa vita, kwani inashughulikia wigo kamili wa masafa ya redio, badala ya kuhitaji antena nyingi kufunika bendi tofauti za masafa, na ni nyeti sana na sahihi kugundua safu pana ya ishara muhimu. Uwezo wa kuondoa haja ya sensorer nyingi pia hufanya kuwa muhimu katika teknolojia ya satelaiti. Kwa sababu ya hali ya hali ya juu, sensorer ya Rydberg inaweza kufanya kazi bila sehemu yoyote ya chuma, ambayo inaweza kutawanya uwanja wa masafa ya redio na sensorer ya atomiki inapatikana kupitia mwanga wa laser, badala ya haja ya nyaya za umeme. Muundo huo mpya uliotengenezwa na timu ya wanasayansi wa Otago ni wa kubebeka na unaweza kuchukuliwa nje ya maabara. Katika maonyesho ya kwanza nje ya maabara, sensor ilikuwa na uwezo wa kupima kwa ufanisi mashamba katika umbali wa mita 30 kwa kutumia kiungo cha laser cha freespaces, na kuongeza kubadilika muhimu kwa teknolojia za utambuzi wa Rydberg-atom. Timu hiyo ilitoa maelezo ya kina ya maendeleo ya sensor mpya na maonyesho yake katika karatasi ambayo ilichapishwa hivi karibuni katika Applied Physics Letters. "Kuchukua hatua zaidi ya maabara na vizuizi vya kimwili: Kazi ya 2012 ya Sedlecek et al. """ Katika utafiti wake, alionyesha matumizi ya Rydberg-excited 87Rb atomu katika kioo mvuke kiini kama detector nyeti kwa ajili ya mashamba microwave. Katika mpango wao, uwepo na nguvu ya mnururisho wa microwave resonant na mpito kati ya hali mbili za Rydberg zilipimwa kwa kutuma kupinga-kueneza nyuzi za laser za bluu na infrared kupitia seli ya mvuke. Kwa kutokuwepo kwa mionzi ya microwave, mwanga wa kuunganisha wa bluu utaanzisha uwazi wa umeme (EIT) kwa mwangaza wa infrared, wakati uwanja wa microwave unaokuja wa amplitude ya mara kwa mara utagawanya kilele cha maambukizi ya EIT katika mbili, na kutoka kwa kutenganisha kilele cha kilele cha Autler-Townes (AT) inaweza kuelezwa. Kwa sababu mabadiliko ya atomu ziko katika moyo wa mpango huu wa majaribio rahisi, inatoa SI traceable na calibration bure electrometry. Katika miaka ya 1990 na 1990, utafiti wa kwanza wa Sedlacek ulifanyika. alishuhudia maendeleo kadhaa. Kwa mfano, unyeti wa on-resonant EIT-AT mbinu inaweza kuwa sana kuboreshwa kwa kutumia superheterodyne mpokeaji usanifu na optical ground-state repumping mbinu, na kufanya hivyo inawezekana kugundua mashamba chini ya 5 μV m < 1. Katika hali ya juu, katika nguvu kubwa za uwanja wa RF, kugawanyika kwa AT sio tena linear na nguvu ya uwanja uliotumika kwa sababu ya mabadiliko ya AC Stark, ambayo hupanda kama nguvu ya uwanja. Badala yake, mabadiliko haya yanaweza kupimwa ili kugundua nguvu za uwanja wa maeneo makubwa ya kutosha. Kupima AC Stark shift pia inaruhusu kugundua masafa nje ya seti tofauti ya mabadiliko ya Rydberg ya atomiki, kupanua mbinu hiyo kwa wigo wa RF ya kuendelea. "Ridberg-atomic systems for communication ni matumizi maalum ambayo hutumia mbinu ya Sedlecek et al. na kanuni za msingi za kazi za mawasiliano ya analog na digital zimeonyeshwa katika mfumo mbalimbali wa msingi wa atomu.""" Ingawa mifumo iliyotajwa hapo juu inaruhusu aina kubwa ya vipimo vya RF na matumizi, karibu mara zote zinahitajika kwenye meza ya macho katika maabara kutokana na mahitaji ya kuunganisha nyuzi mbili (au zaidi) za laser ndani ya chembe ya mvuke ya atomiki. Timu ya Otago iliunda seti ya uthibitisho wa dhana inayoweza kuongeza mwendo, ikibadilisha ufikiaji wa nyuzi kwa seli ya mvuke na miale miwili ya laser ya freespaces na reflector ya prism ya pembe ya cubic, ambayo inaonyesha mhimili wa probe nyuma kwa photodetector. Kwa hivyo, kwa urahisi, chombo cha RF cha atomiki kinaweza kutumiwa kugundua uwanja kwa umbali wa mita 30 kutoka kwa vifaa vya kazi, kama vile laser na photodetector. Picha ya 1 inaonyesha schematic ya seti ya majaribio, kuonyesha kituo cha msingi na transducer tofauti portable, katika zifuatazo inajulikana kama "sensing kitengo," na pia inaonyesha ni ngazi husika atomiki ya 87Rb kushiriki katika RF-to-optical transduction. Kituo cha msingi kina vifaa vyote vinavyohitajika kuandaa uwanja wa mwanga wa EIT ya Rydberg ya fotoni mbili, yaani, laser ya kuunganisha na probe, vifaa vya umeme vya dereva, na kuanzisha kwa ajili ya utulivu wa masafa ya lasers mbili. Kwa mfano, laser ya kuunganisha ina urefu wa mawimbi ya 480nm na nguvu ya juu ya 10 mW. Baada ya kupita kupitia expander beam, beam kuunganisha ina kipenyo beam ya ~ 6mm, sambamba na urefu Rayleigh ya karibu 60m. kwa sehemu ya maonyesho, laser kuunganisha ni imara kwa cavity high-finesse kutumia Pound-Drewer-Hall mbinu, ambayo husababisha mzizi-mean mraba (RMS) linewidth chini ya 100kHz. "Kwenye sehemu ya juu ya sehemu ya chini ya sehemu ya chini ya sehemu ya chini ya sehemu ya chini ya sehemu ya chini ya sehemu ya chini ya sehemu ya chini ya sehemu ya chini ya sehemu ya chini ya sehemu ya chini ya sehemu ya chini ya sehemu ya chini ya sehemu ya chini ya sehemu ya chini ya sehemu ya chini ya sehemu ya chini ya sehemu ya chini ya sehemu ya chini ya sehemu ya chini ya sehemu ya chini ya sehemu ya chini ya sehemu ya chini ya sehemu ya chini ya sehemu ya chini ya sehemu ya chini ya sehemu ya chini ya sehemu ya chini ya sehemu ya chini ya ""Thorlabs PS975A.""" Prism reflector inaruhusu sisi kukaribisha jozi mbili za counter-propagating probe na kuunganisha beams, kupita kupitia kiini mvuke na juhudi ndogo alignment. Wakati kuunganishwa na hali Rydberg kupitia optical mbili-photon mpito, atomu rubidium kuwa nyeti kwa mnururisho wa RF. Hasa, hii hutokea kwa ajili ya masafa ya RF kwamba jozi ngazi Rydberg resonantly kwa ngazi nyingine jirani Rydberg. Kwa mashamba makubwa ya kutosha, atomu ni receptive kwa mbalimbali ya ishara RF kupitia AC Stark mabadiliko. Antenna ya spiral ya nyumbani ya AM (Amplitude Modulated Microwave) inaonyesha frequency ya 16 GHz hadi 20 GHz. Antenna hiyo hutoa mawimbi ya mawimbi madogo yenye umbo la mviringo kando ya mhimili wa mviringo. AM ishara ni imprinted juu ya probe mwanga uwanja kupitia atomu na ni retrieved kutoka light uwanja katika kituo cha msingi kwa kutumia photo detector na spectrum analyzer. Utafiti huu na maonyesho ya maonyesho ya maonyesho ya maonyesho ya maonyesho ya maonyesho ya maonyesho ya maonyesho ya maonyesho ya maonyesho ya maonyesho ya maonyesho ya maonyesho ya maonyesho ya maonyesho ya maonyesho ya maonyesho ya maonyesho ya maonyesho ya maonyesho ya maonyesho ya maonyesho ya maonyesho ya maonyesho ya maonyesho ya maonyesho. Watafiti hao wanasema kazi yao ina changamoto sawa na zile za magnetometers za atomiki zinazotumiwa kwa njia ya mbali, ambazo hufanya kazi kwa njia sawa na detector ya mawimbi madogo ya Rydberg. A bure-nafasi optical kuanzisha, kama kujadiliwa katika kazi hii, ni husika kwa mifumo hii, ingawa polarization-kuhifadhi retroreflector inaweza kuwa zinahitajika. Watafiti wanafikiria maendeleo haya hatimaye kufanya sensorer za quantum kuwa na nguvu zaidi na gharama nafuu, kuwezesha kuhamia nje ya maabara na kuingia katika ulimwengu halisi. - J. Sedlacek, A. Schwettmann, H. Kübler, R. Löw, T. Pfau, na J. Shaffer, Nat. Fizikia. 819 (2012). "Hii ni kwa sababu ya ""mfano wa "" (mfano wa ""mfano wa "") "" (mfano wa ""mfano wa """) ni "" (mfano wa """) "" (mfano wa "") "" (mfano wa """) "" (mfano wa """") "" (mfano wa """) "" (mfano wa """) " A. Gordon, A. Dienstfrey, D. A. Anderson, na G. Raithel, J. Appl. Fizikia. 12236 (mwaka 2017). """Manyuko ya makala hii yalitolewa na Chuo Kikuu cha Otago na sehemu ya karatasi iliyochapishwa na timu ya wataalamu wa fizikia katika Applied Physics Letters." Kwa habari zaidi, tembelea hapa.