Abstract We describe the design, implementation and performance of a compact microcontroller-based time interval/correlation measurement device suitable for characterizing light in quantum optics experiments. It is also suitable for measuring the lifetime of atoms excited by a laser pulse. This correlator is based on measuring the time between the arrival of two consecutive photons and generating a histogram of time between photons. The interferometer is capable of measuring time difference with a resolution of at least 110 ps. The two-photon correlator discussed here was built using an analogue feature within a 16 bit PIC microcontroller whereby the charge on a capacitor is measured. The arrival of the first photon starts the charging and the second photon stops it. The voltage on the capacitor is then proportional to the time difference in the arrival of the two photons. This feature within the microcontroller is called a charge time measurement unit. The system consists of three parts. The first part, made up of two microcontrollers, performs time-to-amplitude conversions using the charge time measurement units and keeps a count of the total number of photons detected by the single-photon detectors. The second part consists of separate circuitry to detect coincidence events using logic gates. The third part consists of a control gateway in the form of another microcontroller between the time measurement microcontrollers and the control software running on a user PC. The system was tested in a lab using simulated signals from a signal generator and in a live quantum optics experiment where our system was compared with a commercial product.
Abstract We describe the design, implementation and performance of a compact microcontroller-based time interval/correlation measurement device suitable for characterizing light in quantum optics experiments. It is also suitable for measuring the lifetime of atoms excited by a laser pulse. This correlator is based on measuring the time between the arrival of two consecutive photons and generating a histogram of time between photons. The interferometer is capable of measuring time difference with a resolution of at least 110 ps. The two-photon correlator discussed here was built using an analogue feature within a 16 bit PIC microcontroller whereby the charge on a capacitor is measured. The arrival of the first photon starts the charging and the second photon stops it. The voltage on the capacitor is then proportional to the time difference in the arrival of the two photons. This feature within the microcontroller is called a charge time measurement unit. The system consists of three parts. The first part, made up of two microcontrollers, performs time-to-amplitude conversions using the charge time measurement units and keeps a count of the total number of photons detected by the single-photon detectors. The second part consists of separate circuitry to detect coincidence events using logic gates. The third part consists of a control gateway in the form of another microcontroller between the time measurement microcontrollers and the control software running on a user PC. The system was tested in a lab using simulated signals from a signal generator and in a live quantum optics experiment where our system was compared with a commercial product.
We used a microcontroller-based setup for the data acquisition in a down-conversion experiment to detect single photon events. This type of setup allows us to compare the effect of the detector's dead time as well as the delay in the data acquisition on the measured data. By using various time windows for the single-photon data acquisition, we estimate the magnitude of the errors in the measuring process as a function of the correlation between the electronics delay and the detector's dead time. Our conclusions are validated by analyzing the particle number, detection rates, and statistical distributions, as well as the correlations between signal and idler photons.
Time-correlated photons can be used to demonstrate emerging technical applications such as ghost imaging, and they can demonstrate quantum-based phenomena in order to interest undergraduate students in engineering applications involving optics and quantum mechanics. In this work, we use spontaneous parametric down-conversion to generate time-correlated photons. To achieve this, we simulated laboratory parameters with MATLAB and designed optical and electrical setups. Specifically, we used a 405 nm diode laser, various common optical components, and a nonlinear crystal designed to generate time-correlated photons, and we used single-photon detectors, time-to-amplitude converters, custom flash-conversion analog-to-digital converters, a Teensy 4.1 microcontroller, and the Arduino IDE to detect the time-correlated photons. We present two significant results. First, we measured >100,000 counts per second 5 ± 1° on either side of our input laser which was within our theoretical expectations of 4–9° and much greater than our < 2000 dark counts per second. Our second major result was finding 15.8 ± 0.7 time-correlated counts per second with an SNR of 2.7. We also outline future extensions of our work including ghost imaging and generating polarization-entangled photons.
Summary form only given. In any optical system, quantum and classical theory yield identical predictions for the mean intensity. The quantum mechanical predictions diverge from the classical theory only for higher order correlations. For this reason, typical quantum-interference experiments are performed by measuring coincidence rates between two or more detectors. The usual approximation, following Glauber, is that a single-photon counter fires at a rate proportional to the intensity, or number of incident photons per unit time. This approximation is so good and so entrenched that one routinely assumes that all singles-detection rates are insensitive to quantum effects. However, if one of these detectors fires, it cannot fire again for a characteristic time, called the dead-time. This characteristic of the detectors makes them highly nonlinear over times shorter than the dead-time, and thus sensitive to the higher order intensity correlations. In other words the detector has a different response for two photons arriving at different times, than for two photons arriving at the same time. We use the process of spontaneous parametric-downconversion (SPDC) to create correlated photon-pairs and send them through a polarization-based Hong-Ou-Mander interferometer. This quantum interferometer allows us to change the photon statistics without changing the intensity of the beams.
Abstract This paper presents a correlator for constructing the second-order autocorrelation function g(2)(τ), implemented on a field-programmable gate array (FPGA). The device is designed for high-precision recording of time intervals between photons detected from single emitters. The use of an FPGA makes it possible to achieve a time resolution of 185 ps and real-time event processing. Experimental data confirming the achievement of photon antibunching with g(2)(0) < 0.5, characteristic of single quantum emitters, are demonstrated. The device can be used to analyze photon correlations in quantum optics problems and when working with single quantum emitters.
In this study of quantum optics, we want to extract information associated with quantum mechanically entangled photon pairs. Measurements involved here take advantage of the fact that the photon pairs, created at the same point in space and time, will arrive “in coincidence” at detectors placed equally far from the source. Conservation of momentum also constrains the placement of these detectors. These effects, in combination, allow us to differentiate between these entangled photons and other stray photons that may reach the detectors. Initial efforts have included building a more stable laser mount, studying parametric down conversion (the process of converting the single beam into the entangled photon pairs), and establishing a small time interval for coincidence detection. For this, we explore the consequences of moving away from a Field Programmable Gate Array (FPGA) for coincidence measurements and towards the use of a Programmable System on a Chip (PSoC), which essentially combines the fast digital logic gates of an FPGA with micro-controller functionality. We are gaining hands-on experience with some highly theoretical aspects intrinsic to quantum mechanics, expanding upon laboratory setups described in Mark Beck’s recent text on quantum mechanics, as well as materials from Exploring Quantum Physics through Hands-On Projects by David Prutchi and Shanni R. Prutchi.
Photon correlated beams, generated by parametric down-conversion in nonlinear crystals (PDC), have been proved successfully for the measurement of quantum efficiency, of single photon detectors [1, 2, 3, 4] and can be used for measuring transmittance, as well. The main feature relies on the realization of two correlated quantum channels yielding coincident events. To reduce uncertainty [4, 5, 6] and determine its ultimate limit, contributions to statistical noise in a real experimental set-up are here investigated, and a general model is proposed to calculate the maximum likelihood best estimators and evaluate the probability of coincidence. In typical measurement scheme a channel is set as trigger (idler, i) and attention is paid to catch at least the same amount of correlated photons in the other channel (signal, s) [4]. Unwanted uncorrelated photons due to PDC itself result in a decreased degree of correlation, noise fluctuations in coincidence measurements and asymmetry between the two channels, whose mean photon rate can be quite different. We indicate by with the mean rate of correlated photons in s and i channels We address the total mean photon rates in both channels as where terms take into account also additive background photon rates due to straylight and detector noise. Actually statistical noise is also due to losses of correlated photons by optical elements, non ideal detectors and electronic devices in both channels. We distinguish, therefore, between optical losses ( transmittance of the correlated photon path), detection losses detectorquantum efficiency), electronic losses associated to the dead times time during which the detection system is unable to detect photons). It is usual to identify dead times as non-extending and extending: in the first case, all photons following a revealed photon within the fixed time interval are ignored, while in the second case any incoming photon produces or prolongs Eventually the finite duration of the time coincidence window, modifies the distribution probability of coincident events. Let us consider the distribution probability of single channel