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arXiv:2403.08674 · Physical Review Research

Quantum jump photodetector for narrowband photon counting with a single atom

Laura Zarraoa, Romain Veyron, Tomas Lamich, Lorena C. Bianchet, Morgan W. Mitchell

Published Sep 26, 2024• 2 citations
arXivHTMLPDF

Abstract

Using a single neutral Rb 87 atom held in an optical trap, and “quantum jump” detection of single-photon-initiated state changes, we demonstrate a single-photon quantum jump photodetector (QJPD) with intrinsically narrow bandwidth and strong rejection of out-of-band photons, of interest for detecting weak optical signals in the presence of a strong broadband background. By analyzing fluorescence photon count distributions for the bright and dark states with and without excitation, we measure quantum efficiency of 2.9 ( 2 ) × 10 − 3 , a record for single-pass quantum jump production, and signal-photon-unprovoked “dark jump” rate—analogous to the dark count rate of other detectors —of 3 ( 10 ) × 10 − 3 jumps / s during passive accumulation plus 4.0 ( 4 ) × 10 − 3 jumps per readout, orders of magnitude below those of traditional single-photon detectors. Available methods can substantially improve QJPD quantum efficiency, dark jump rate, bandwidth, and tunability. Published by the American Physical Society 2024

DOI
10.1103/physrevresearch.6.033338

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Detection of photon-level signals embedded in sunlight with an atomic photodetector

Laura Zarraoa, Tomas Lamich, Sondos Elsehimy +2 more

The detection of few-photon signals in a broadband background is an extreme challenge for photon counting, requiring filtering that accepts a narrow range of optical frequencies while strongly rejecting all others. Recent work [Zarraoa et. al, Phys. Rev. Res. 6, 033338 (2024)] demonstrated that trapped single atoms can act as low dark-count narrow-band photodetectors. Here we show that this ``quantum jump photodetector'' (QJPD) approach can also detect photon-level signals embedded in strong sunlight. Using a single rubidium atom as a QJPD, we count arrivals of individual narrow-band laser photons embedded in sunlight powers of order $10^{10}$ photons/s. We derive a rate-equation model for the atom's internal-state dynamics in sunlight, and find quantitative agreement with experiment. Using this model, we calculate the channel capacity over a noisy communication channel when sending weak coherent states and detecting them in the presence of sunlight, achieving a representative rate of 0.5 bits per symbol when sending 150 probe photons per 10 ms time-bin, embedded in 1 nW of sunlight (of order $10^{10}$ photons/s in the visible and near-infrared bands). The demonstration may benefit background-limited applications such as daytime light detection and ranging (LIDAR), remote magnetometry, and free-space classical and quantum optical communications.

quant-pharXiv:2512.02521•AVS Quantum Science•Dec 3, 2025•0 citations

Photon counting with a single neutral atom: quantum efficiency, dark counts, and background rejection

Laura Zarraoa

(English) This thesis studies the use of a single trapped neutral 87Rb atom as a photon counter. Detection of quantum jumps (QJs), i.e., abrupt changes between atomic states observable by a change in atomic fluorescence, is used to infer the arrival of single photons. This is referred to as the quantum jump photodetection (QJPD) technique. The thesis first situates QJPD in the context of photodetection. Compared to traditional detectors, QJPD technique has lower speed and quantum efficiency (QE), but has exceptional performance in other figures of merit: QJPD is intrinsically narrowband, has strong out-of-band rejection, and very low dark counts (DCs). These features make the QJPD interesting for applications that detect weak optical signals in the presence of a strong broadband background. Experimental methods to study QJPD are described. A 87Rb atom is loaded from a magneto-optical trap (MOT) into a far-off resonance trap (FORT) at the center of four orthogonal, co-focal, high numerical aperture lenses. These lenses create the FORT, couple probe light onto the atom and collect the atomic fluorescence, which is used to identify the atomic state. A typical QJPD sequence is presented, which consists of trapping and cooling an atom in the FORT, optically pumping it into the dark state, illuminating with probe light, illuminating with readout light and collecting fluorescence photons, and checking that the atom has not left the FORT during the sequence. Statistical methods for measurement of QE and DC contributions are introduced. These compare the observed fluorescence count distribution against measured hyperfine-state fluorescence distributions. A QE of (2.4±0.1)×e−3 is demonstrated, a record for single photon absorption by a single atom in free space. Dark count contributions are measured. To produce low DC, the QJPD technique is implemented in two time windows: an exposure time for the single photon absorption followed by a short fluorescence time to read out the atomic state. This implies distinct acquisition and readout DC contributions, similarly to CCD and CMOS detectors. A dark jump rate (analogous to CCD/CMOS dark current) is measured of (5 ± 10) × e−3 jumps/s, consistent with zero and limited by measurement statistics. The measured readout contribution is (4.0 ± 0.4) × e−3 jumps per ms of fluorescence readout. For a 1 Hz readout rate, with 1 ms readout pulses, a net dark count rate of (15 ± 10) × e−3 counts/acquisition is demonstrated, which is already competitive with any non-cryogenic detector. The background rejection capabilities of the system are tested by measuring quantum jump rates when the atom is illuminated with direct sunlight, and with light scattered by the atmosphere (skylight). A rate equation model is developed to describe QJ probabilities in the presence of both intense broadband background and weak resonant probe light. This model is used to interpret experiments in which a weak signal beam competes with strong broadband background and validated using direct sunlight. Measurements where the atom is illuminated with skylight show no observable background-induced QJs. Finally, measurements of sky brightness and its fluctuations are presented, showing large fluctuations even on mostly clear days, a factor that further increases the need for background rejection. A number of contemporary applications of extreme photodetection, including free-space quantum communication in daylight, classical optical communications in space, and fundamental physics experiments, are discussed as possible applications of the QJPD technique. A realistic scenario where the demonstrated QJPD capabilities surpass the current performance of commercial single photodetectors is presented. Finally, potential improvements are discussed. It is shown that existing atomic and optical technologies could be applied to reach different wavelength ranges, narrower bandwidths, higher quantum efficiency, and lower dark counts. (Català) Aquesta tesi estudia l’ús d’un sol àtom neutre de Rubidio 87 atrapat com a comptador de fotons. La detecció de salts quàntics (QJs), canvis abruptes entre estats atòmics observables per canvis de fluorescència, es fa servir per inferir l'arribada de fotons únics. A aquesta tècnica l‘anomenem fotodetecció per salts quàntics (QJPD). Aquesta tesi primer situa la QJPD en el context de la fotodetecció. Comparada amb detectors tradicionals, la tècnica QJPD té una menor velocitat i menor eficiència quàntica (QE), però resulta excepcional per ser intrínsecament de banda estreta i per tenir un fort rebuig de fotons fora de banda i molt baixos comptes foscos (DCs). Aquestes característiques fan que sigui interessant per a aplicacions que detecten senyals òptics febles en presència de llum de fons de banda ampla. Els mètodes experimentals consisteixen en carregar un àtom de Rb87 des d'un parany magneto-òptic (MOT) a un parany fora de ressonància (FORT) localitzada al centre de quatre lents ortogonals, co-focals i d'alta obertura numèrica. Aquestes lents creen la FORT, acoblen la llum de prova a l'àtom i recullen la fluorescència atòmica, que és usada per identificar l'estat atòmic. La seqüència de QJPD consisteix a atrapar i refredar un àtom a la FORT, bombar-lo a l'estat fosc, il·luminar-lo amb llum de prova, il·luminar-lo amb llum de lectura i recollir la fluorescència, i comprovar que l'àtom no ha abandonat la FORT. S'introdueixen mètodes estadístics per mesurar la QE i les DC que comparen la distribució de comptes de fluorescència observada amb les distribucions de fluorescència de l'estat hiperfí. Es demostra una QE de (2.4±0.1)×e−3, un rècord per a l'absorció d'un sol fotó per un sol àtom en espai lliure. S’hi mesuren les contribucions dels DC. Per produir DC baixos, la QJPD s'implementa en dos temps: un temps d'exposició per absorció del fotó únic seguit d'un curt temps de fluorescència per llegir l'estat atòmic. Això implica contribucions a les DC diferenciades de adquisició i lectura, com passa als detectors CCD i CMOS. La taxa de salts foscos (anàloga al corrent fosc dels CCD/CMOS) és de (5 ± 10) × e−3 salts/s, compatible amb zero i limitada per les estadístiques de la mesura. La contribució de lectura és de (4.0 ± 0.4) × e−3 salts per ms de fluorescència. Per a una freqüència de lectura de 1 Hz, amb polsos de lectura de 1 ms, es demostra una taxa neta de DC de (15 ± 10) × e−3 comptes\ adquisición, que ja és competitiva amb qualsevol detector no criogènic. Les capacitats de rebuig de llum de Fons (LF) es comproven mesurant la taxa de QJs quan l'àtom és il·luminat amb llum solar directa i amb llum dispersada per l'atmosfera (llum celestial). Es desenvolupa un model d'equacions cinètiques que descriure les probabilitats de QJs en presència de LF de banda ampla, alhora que amb llum de prova feble en ressonància. Aquest model interpreta els experiments en què un feix de senyal feble competeix contra forta LF de banda ampla i es valida utilitzant llum solar directa. Experimentalment, no s'observen QJs induïts per la llum celestial. S’hi mesuren també la brillantor de la llum celestial i les seves fluctuacions, que resulten grans fins i tot en dies majoritàriament clars, factor que augmenta encara més la necessitat de rebutjar la LF. S’hi discuteixen diverses aplicacions extremes de fotodetecció contemporànies com a possibles aplicacions per a la QJPD, incloent comunicacions quàntiques en espai lliure durant el dia, comunicacions clàssiques a l'espai i experiments de física fonamental. Es presenta un escenari en què l'exercic de la QJPD sobrepassen el de detectors comercials. Finalment, s’hi discuteixen millores potencials. Es demostra que tecnologies atòmiques i òptiques existents poden ser aplicades per assolir diferents rangs de longitud d'ona, amples de banda més estrets, eficiència quàntica més alta i comptes foscos més baixos. (Español) Esta tesis estudia el uso de un solo átomo neutro de 87Rb atrapado como contador de fotones. La detección de saltos cuánticos (QJs), cambios abruptos entre estados atómicos observables por cambios de fluorescencia, se usa para inferir la llegada de fotones únicos. A esta técnica la nombramos fotodetección por saltos cuánticos (QJPD). Esta tesis primero sitúa la QJPD en el contexto de la fotodetección. Comparada con detectores tradicionales, la QJPD tiene una menor velocidad y menor eficiencia cuántica (QE), pero resulta excepcional por ser intrínsecamente de banda estrecha y por tener un fuerte rechazo de fotones fuera de banda y muy bajas cuentas oscuras (DCs). Estas características hacen que sea interesante para aplicaciones que detectan señales ópticas débiles en presencia de luz de fondo de banda ancha. Los métodos experimentales consisten en cargar un átomo de 87Rb desde una trampa magneto-óptica (MOT) a una trampa fuera de resonancia (FORT) localizada en el centro de cuatro lentes ortogonales, co-focales y de alta apertura numérica. Estas lentes crean la FORT, acoplan la luz de prueba al átomo y recogen su fluorescencia, que se usa para identificar el estado atómico. La secuencia de QJPD consiste en atrapar y enfriar un átomo en la FORT, bombearlo al estado oscuro, iluminarlo con luz de prueba, iluminarlo con luz de lectura y recoger la fluorescencia, y comprobar que el átomo no ha abandonado la FORT. Se introducen métodos estadísticos para medir la QE y las DC que comparan la distribución de cuentas de fluorescencia observada con las distribuciones de fluorescencia de los estados hiperfinos. Se demuestra una QE de (2.4±0.1)×e−3, un récord para la absorción de un solo fotón por un solo átomo en espacio libre. Se miden las contribuciones a las DC. Para lograr un nivel muy bajo de DC, la QJPD se implementa en dos tiempos: uno de exposición para la absorción del fotón único seguido de un corto tiempo de fluorescencia para leer el estado atómico. Esto implica contri

•Feb 27, 2025•0 citations

Engineering quantum jump superoperators for single-photon detectors

Alexandre V. Dodonov, Salomon Sylvain Mizrahi, V. V. Dodonov

We study the back action of a single-photon detector on the electromagnetic field upon a photodetection by considering a microscopic model in which the detector is constituted of a sensor and an amplification mechanism. Using the quantum trajectories approach we determine the quantum jump superoperator (QJS) that describes the action of the detector on the field state immediately after the photocount. The resulting QJS consists of two parts: the bright-count term, representing the real photoabsorptions, and the dark-count term, representing the amplification of intrinsic excitations inside the detector. First we compare our results for the counting rates to experimental data, showing good agreement. Then we point out that by modifying the field frequency one can engineer the form of the QJS, obtaining the QJS's proposed previously in an ad hoc manner.

arXiv:quant-ph/0601037•Physical Review A•Sep 29, 2006•16 citations

Macroscopic quantum jumps in a single atom

Axel Schenzle, Richard G. Brewer

A single-atom optical clock proposed over ten years ago utilizes an amplification scheme which only recently was recognized as a novel problem in quantum statistics. The atom, a three-state system, has two coupled transitions that are driven continuously by two external fields, one being an allowed transition (1\ensuremath{\leftrightarrows}3) and the other a forbidden transition (2\ensuremath{\leftrightarrows}3) where \ensuremath{\Vert}3〉 is the lowest state. It has been argued that the weak transition, which is difficult to detect, could be monitored by the presence or absence of spontaneous emission of the strong transition. Thus, when the atom is shelved in the metastable state \ensuremath{\Vert}2〉, the strong transition is extinguished, but when the atom executes a single quantum jump (2\ensuremath{\rightarrow}3), it triggers a succession of perhaps a million quantum jumps (macroscopic quantum jumps) in the strong transition, an amplification that can be detected easily. This intuitive argument for alternating bright and dark intervals assumes, however, that the atom is always in an eigenstate. Should the atom be in a superposition state, because of coherent excitation, one could imagine that the weak transition would merely reduce the intensity of the strong transition slightly. This issue is resolved, in favor of the first intuitive argument, by calculating the photon-counting statistics, the probability W(n,T) of observing precisely n photon-counting events in a collection T in a quantum-mechanically consistent way. The results cannot be described by classical statistics. A compact analytic form is obtained for W(n,T) by considering the entire hierarchy of correlation functions where the emission interval peaks sharply about a particular n with a Poisson distribution and can be comparable in length to the darkness interval (n=0) while the other values of n display vanishingly small probabilities.

Physical Review A•Oct 1, 1986•93 citations

SUPERCONDUCTING SINGLE-PHOTON DETECTION

Guo Guang-Can

Single-photon detection,which is the core of weak light detection,plays key role in the fields of quantum information,physics,biology,chemistry and astronomy.The low sensibility and the high dark count rate of traditional single-photon detectors which base on photomultiplier tube or avalanche photodiode limit the improvement of the signal noise ratio and the low counting rate limits the detecting speed and the dynamic range.Here we review the single-photon detecting technology using superconducting materials as light sensitive apparatus.Their quantum efficiency,dark count rate and counting rate outclass the traditional single-photon detector.Their appearances certainly will bring a great influence to the subjects relating to the single-photon detection.

Progress in physics•Jan 1, 2007•0 citations

Quantum jump spectroscopy of a single neutral atom for precise subwavelength intensity measurements

Lorena C. Bianchet, Natália Alves, Laura Zarraoa +3 more

A single trapped neutral atom is used for precise subwavelength intensity measurements. Quantum jumps from a dark to a bright atomic state are used to boost signal-to-noise and avoid systematic errors.

Physical Review Research•Nov 14, 2022•7 citations
Using a single neutral Rb 87 atom held in an optical trap, and “quantum jump” detection of single-photon-initiated state changes, we demonstrate a single-photon quantum jump photodetector (QJPD) with intrinsically narrow bandwidth and strong rejection of out-of-band photons, of interest for detecting weak optical signals in the presence of a strong broadband background. By analyzing fluorescence photon count distributions for the bright and dark states with and without excitation, we measure quantum efficiency of 2.9 ( 2 ) × 10 − 3 , a record for single-pass quantum jump production, and signal-photon-unprovoked “dark jump” rate—analogous to the dark count rate of other detectors —of 3 ( 10 ) × 10 − 3 jumps / s during passive accumulation plus 4.0 ( 4 ) × 10 − 3 jumps per readout, orders of magnitude below those of traditional single-photon detectors. Available methods can substantially improve QJPD quantum efficiency, dark jump rate, bandwidth, and tunability. Published by the American Physical Society 2024
The detection of few-photon signals in a broadband background is an extreme challenge for photon counting, requiring filtering that accepts a narrow range of optical frequencies while strongly rejecting all others. Recent work [Zarraoa et. al, Phys. Rev. Res. 6, 033338 (2024)] demonstrated that trapped single atoms can act as low dark-count narrow-band photodetectors. Here we show that this ``quantum jump photodetector'' (QJPD) approach can also detect photon-level signals embedded in strong sunlight. Using a single rubidium atom as a QJPD, we count arrivals of individual narrow-band laser photons embedded in sunlight powers of order 101010^{10}1010 photons/s. We derive a rate-equation model for the atom's internal-state dynamics in sunlight, and find quantitative agreement with experiment. Using this model, we calculate the channel capacity over a noisy communication channel when sending weak coherent states and detecting them in the presence of sunlight, achieving a representative rate of 0.5 bits per symbol when sending 150 probe photons per 10 ms time-bin, embedded in 1 nW of sunlight (of order 101010^{10}1010 photons/s in the visible and near-infrared bands). The demonstration may benefit background-limited applications such as daytime light detection and ranging (LIDAR), remote magnetometry, and free-space classical and quantum optical communications.
(English) This thesis studies the use of a single trapped neutral 87Rb atom as a photon counter. Detection of quantum jumps (QJs), i.e., abrupt changes between atomic states observable by a change in atomic fluorescence, is used to infer the arrival of single photons. This is referred to as the quantum jump photodetection (QJPD) technique. The thesis first situates QJPD in the context of photodetection. Compared to traditional detectors, QJPD technique has lower speed and quantum efficiency (QE), but has exceptional performance in other figures of merit: QJPD is intrinsically narrowband, has strong out-of-band rejection, and very low dark counts (DCs). These features make the QJPD interesting for applications that detect weak optical signals in the presence of a strong broadband background. Experimental methods to study QJPD are described. A 87Rb atom is loaded from a magneto-optical trap (MOT) into a far-off resonance trap (FORT) at the center of four orthogonal, co-focal, high numerical aperture lenses. These lenses create the FORT, couple probe light onto the atom and collect the atomic fluorescence, which is used to identify the atomic state. A typical QJPD sequence is presented, which consists of trapping and cooling an atom in the FORT, optically pumping it into the dark state, illuminating with probe light, illuminating with readout light and collecting fluorescence photons, and checking that the atom has not left the FORT during the sequence. Statistical methods for measurement of QE and DC contributions are introduced. These compare the observed fluorescence count distribution against measured hyperfine-state fluorescence distributions. A QE of (2.4±0.1)×e−3 is demonstrated, a record for single photon absorption by a single atom in free space. Dark count contributions are measured. To produce low DC, the QJPD technique is implemented in two time windows: an exposure time for the single photon absorption followed by a short fluorescence time to read out the atomic state. This implies distinct acquisition and readout DC contributions, similarly to CCD and CMOS detectors. A dark jump rate (analogous to CCD/CMOS dark current) is measured of (5 ± 10) × e−3 jumps/s, consistent with zero and limited by measurement statistics. The measured readout contribution is (4.0 ± 0.4) × e−3 jumps per ms of fluorescence readout. For a 1 Hz readout rate, with 1 ms readout pulses, a net dark count rate of (15 ± 10) × e−3 counts/acquisition is demonstrated, which is already competitive with any non-cryogenic detector. The background rejection capabilities of the system are tested by measuring quantum jump rates when the atom is illuminated with direct sunlight, and with light scattered by the atmosphere (skylight). A rate equation model is developed to describe QJ probabilities in the presence of both intense broadband background and weak resonant probe light. This model is used to interpret experiments in which a weak signal beam competes with strong broadband background and validated using direct sunlight. Measurements where the atom is illuminated with skylight show no observable background-induced QJs. Finally, measurements of sky brightness and its fluctuations are presented, showing large fluctuations even on mostly clear days, a factor that further increases the need for background rejection. A number of contemporary applications of extreme photodetection, including free-space quantum communication in daylight, classical optical communications in space, and fundamental physics experiments, are discussed as possible applications of the QJPD technique. A realistic scenario where the demonstrated QJPD capabilities surpass the current performance of commercial single photodetectors is presented. Finally, potential improvements are discussed. It is shown that existing atomic and optical technologies could be applied to reach different wavelength ranges, narrower bandwidths, higher quantum efficiency, and lower dark counts. (Català) Aquesta tesi estudia l’ús d’un sol àtom neutre de Rubidio 87 atrapat com a comptador de fotons. La detecció de salts quàntics (QJs), canvis abruptes entre estats atòmics observables per canvis de fluorescència, es fa servir per inferir l'arribada de fotons únics. A aquesta tècnica l‘anomenem fotodetecció per salts quàntics (QJPD). Aquesta tesi primer situa la QJPD en el context de la fotodetecció. Comparada amb detectors tradicionals, la tècnica QJPD té una menor velocitat i menor eficiència quàntica (QE), però resulta excepcional per ser intrínsecament de banda estreta i per tenir un fort rebuig de fotons fora de banda i molt baixos comptes foscos (DCs). Aquestes característiques fan que sigui interessant per a aplicacions que detecten senyals òptics febles en presència de llum de fons de banda ampla. Els mètodes experimentals consisteixen en carregar un àtom de Rb87 des d'un parany magneto-òptic (MOT) a un parany fora de ressonància (FORT) localitzada al centre de quatre lents ortogonals, co-focals i d'alta obertura numèrica. Aquestes lents creen la FORT, acoblen la llum de prova a l'àtom i recullen la fluorescència atòmica, que és usada per identificar l'estat atòmic. La seqüència de QJPD consisteix a atrapar i refredar un àtom a la FORT, bombar-lo a l'estat fosc, il·luminar-lo amb llum de prova, il·luminar-lo amb llum de lectura i recollir la fluorescència, i comprovar que l'àtom no ha abandonat la FORT. S'introdueixen mètodes estadístics per mesurar la QE i les DC que comparen la distribució de comptes de fluorescència observada amb les distribucions de fluorescència de l'estat hiperfí. Es demostra una QE de (2.4±0.1)×e−3, un rècord per a l'absorció d'un sol fotó per un sol àtom en espai lliure. S’hi mesuren les contribucions dels DC. Per produir DC baixos, la QJPD s'implementa en dos temps: un temps d'exposició per absorció del fotó únic seguit d'un curt temps de fluorescència per llegir l'estat atòmic. Això implica contribucions a les DC diferenciades de adquisició i lectura, com passa als detectors CCD i CMOS. La taxa de salts foscos (anàloga al corrent fosc dels CCD/CMOS) és de (5 ± 10) × e−3 salts/s, compatible amb zero i limitada per les estadístiques de la mesura. La contribució de lectura és de (4.0 ± 0.4) × e−3 salts per ms de fluorescència. Per a una freqüència de lectura de 1 Hz, amb polsos de lectura de 1 ms, es demostra una taxa neta de DC de (15 ± 10) × e−3 comptes\ adquisición, que ja és competitiva amb qualsevol detector no criogènic. Les capacitats de rebuig de llum de Fons (LF) es comproven mesurant la taxa de QJs quan l'àtom és il·luminat amb llum solar directa i amb llum dispersada per l'atmosfera (llum celestial). Es desenvolupa un model d'equacions cinètiques que descriure les probabilitats de QJs en presència de LF de banda ampla, alhora que amb llum de prova feble en ressonància. Aquest model interpreta els experiments en què un feix de senyal feble competeix contra forta LF de banda ampla i es valida utilitzant llum solar directa. Experimentalment, no s'observen QJs induïts per la llum celestial. S’hi mesuren també la brillantor de la llum celestial i les seves fluctuacions, que resulten grans fins i tot en dies majoritàriament clars, factor que augmenta encara més la necessitat de rebutjar la LF. S’hi discuteixen diverses aplicacions extremes de fotodetecció contemporànies com a possibles aplicacions per a la QJPD, incloent comunicacions quàntiques en espai lliure durant el dia, comunicacions clàssiques a l'espai i experiments de física fonamental. Es presenta un escenari en què l'exercic de la QJPD sobrepassen el de detectors comercials. Finalment, s’hi discuteixen millores potencials. Es demostra que tecnologies atòmiques i òptiques existents poden ser aplicades per assolir diferents rangs de longitud d'ona, amples de banda més estrets, eficiència quàntica més alta i comptes foscos més baixos. (Español) Esta tesis estudia el uso de un solo átomo neutro de 87Rb atrapado como contador de fotones. La detección de saltos cuánticos (QJs), cambios abruptos entre estados atómicos observables por cambios de fluorescencia, se usa para inferir la llegada de fotones únicos. A esta técnica la nombramos fotodetección por saltos cuánticos (QJPD). Esta tesis primero sitúa la QJPD en el contexto de la fotodetección. Comparada con detectores tradicionales, la QJPD tiene una menor velocidad y menor eficiencia cuántica (QE), pero resulta excepcional por ser intrínsecamente de banda estrecha y por tener un fuerte rechazo de fotones fuera de banda y muy bajas cuentas oscuras (DCs). Estas características hacen que sea interesante para aplicaciones que detectan señales ópticas débiles en presencia de luz de fondo de banda ancha. Los métodos experimentales consisten en cargar un átomo de 87Rb desde una trampa magneto-óptica (MOT) a una trampa fuera de resonancia (FORT) localizada en el centro de cuatro lentes ortogonales, co-focales y de alta apertura numérica. Estas lentes crean la FORT, acoplan la luz de prueba al átomo y recogen su fluorescencia, que se usa para identificar el estado atómico. La secuencia de QJPD consiste en atrapar y enfriar un átomo en la FORT, bombearlo al estado oscuro, iluminarlo con luz de prueba, iluminarlo con luz de lectura y recoger la fluorescencia, y comprobar que el átomo no ha abandonado la FORT. Se introducen métodos estadísticos para medir la QE y las DC que comparan la distribución de cuentas de fluorescencia observada con las distribuciones de fluorescencia de los estados hiperfinos. Se demuestra una QE de (2.4±0.1)×e−3, un récord para la absorción de un solo fotón por un solo átomo en espacio libre. Se miden las contribuciones a las DC. Para lograr un nivel muy bajo de DC, la QJPD se implementa en dos tiempos: uno de exposición para la absorción del fotón único seguido de un corto tiempo de fluorescencia para leer el estado atómico. Esto implica contri
We study the back action of a single-photon detector on the electromagnetic field upon a photodetection by considering a microscopic model in which the detector is constituted of a sensor and an amplification mechanism. Using the quantum trajectories approach we determine the quantum jump superoperator (QJS) that describes the action of the detector on the field state immediately after the photocount. The resulting QJS consists of two parts: the bright-count term, representing the real photoabsorptions, and the dark-count term, representing the amplification of intrinsic excitations inside the detector. First we compare our results for the counting rates to experimental data, showing good agreement. Then we point out that by modifying the field frequency one can engineer the form of the QJS, obtaining the QJS's proposed previously in an ad hoc manner.
A single-atom optical clock proposed over ten years ago utilizes an amplification scheme which only recently was recognized as a novel problem in quantum statistics. The atom, a three-state system, has two coupled transitions that are driven continuously by two external fields, one being an allowed transition (1\ensuremath{\leftrightarrows}3) and the other a forbidden transition (2\ensuremath{\leftrightarrows}3) where \ensuremath{\Vert}3〉 is the lowest state. It has been argued that the weak transition, which is difficult to detect, could be monitored by the presence or absence of spontaneous emission of the strong transition. Thus, when the atom is shelved in the metastable state \ensuremath{\Vert}2〉, the strong transition is extinguished, but when the atom executes a single quantum jump (2\ensuremath{\rightarrow}3), it triggers a succession of perhaps a million quantum jumps (macroscopic quantum jumps) in the strong transition, an amplification that can be detected easily. This intuitive argument for alternating bright and dark intervals assumes, however, that the atom is always in an eigenstate. Should the atom be in a superposition state, because of coherent excitation, one could imagine that the weak transition would merely reduce the intensity of the strong transition slightly. This issue is resolved, in favor of the first intuitive argument, by calculating the photon-counting statistics, the probability W(n,T) of observing precisely n photon-counting events in a collection T in a quantum-mechanically consistent way. The results cannot be described by classical statistics. A compact analytic form is obtained for W(n,T) by considering the entire hierarchy of correlation functions where the emission interval peaks sharply about a particular n with a Poisson distribution and can be comparable in length to the darkness interval (n=0) while the other values of n display vanishingly small probabilities.
Single-photon detection,which is the core of weak light detection,plays key role in the fields of quantum information,physics,biology,chemistry and astronomy.The low sensibility and the high dark count rate of traditional single-photon detectors which base on photomultiplier tube or avalanche photodiode limit the improvement of the signal noise ratio and the low counting rate limits the detecting speed and the dynamic range.Here we review the single-photon detecting technology using superconducting materials as light sensitive apparatus.Their quantum efficiency,dark count rate and counting rate outclass the traditional single-photon detector.Their appearances certainly will bring a great influence to the subjects relating to the single-photon detection.