#spontaneousparametricdownconversion

New SPDC Source at 900-950nm Improves Single-Photon Generation

Sudden Parametric Down Conversion

Quantum technology has advanced by boosting the possibility of producing crucial single photons by refining a time-multiplexed approach for Spontaneous Parametric Down-Conversion (SPDC). This groundbreaking study examines a quantum SPDC source in the 900–950 nm range under the guidance of V. O. Gotovtsev, I. V. Dyakonov, and O. V. Borzenkova, with help from K. A. Taratorin and T. B. Dugarnimaev. By correctly estimating and modeling heralding efficiency and purity, this study shows how to build brighter and more reliable single-photon sources for future quantum applications.

The Single-Photon Source Foundational Challenge

Single photons are essential for many quantum technologies, but generating them is challenging. A higher-energy pump photon spontaneously divides into two lower-energy photons, called twin photons with associated characteristics, causing SPDC, or parametric fluorescence. This method is used in quantum optics, metrology, computing, cryptography, and fundamental physics rule testing.

SPDC's inefficiency hinders many quantum information and cryptography applications. Probabilistic photon pair creation uses Poisson distribution. Only a small percentage (10−5 to 10−12) of the pump beam is used to make a duplicate pair of down-converted photons, leaving the remainder unmodified. Increasing pump power to boost output also increases the adverse possibility of creating multiple pairs.

Due to this inefficiency, reliable, heralded single-photon sources that signify a single photon when its double is detected are necessary.

Time-multiplexing boosts efficiency

Researchers developed and refined time-multiplexing to overcome poor single photon generation probability. This approach makes photon pairs using SPDC pumped by laser pulses. The idler photon, the entangled companion photon, starts signal photon storage in optical memory, which is the fundamental innovation.

Once the idler photon is recognized, the signal photon is steered into an optical memory cell and stored until the pulse series ends. By increasing the chance to capture a single photon inside a temporal window, this method increases detection likelihood.

The experiment employed a femtosecond laser and an advanced field-programmable gate array to precisely store and release photons. Researchers carefully calculated the likelihood of acquiring a single photon after multiplexing by considering photon pair formation rates and detecting system efficiency. Despite their achievement, the team noted that the optical memory cell's actuation speed limitation required careful multiplexing probability computation. Future optical memory cell advances should focus on speed and capacity.

Domain Engineering Ensures Extra Pure

High purity and generation probability are needed to maximize single-photon source dependability. Purity dictates photon quantum state definition for quantum computing and communication.

Through careful investigation and optimization, the team produced high-purity entangled photon pairs, focusing on SPDC photon pair features. Domain engineering was used to shape the generation nonlinear crystal's interior structure. This engineering targets a consistent, single-mode output that promotes purity by regulating down-conversion.

Domain engineering eliminated spectrum correlations between produced photons, which impair purity, and the phase-matching function should be Gaussian. Selecting the crystal length and using a narrow-bandwidth laser increased purity. Researchers used computer simulations to compare their unique domain structure to traditional designs and found a 10% purity gain.

The optimization process also optimized the heralding probability, given as the photon pairs' joint spectral amplitude. The JSA fully describes the two-photon state and idler-signal spectral correlations. Periodically poled laser-pumped potassium titanyl phosphate (PPKTP) crystals were used in experiments. Experimental results confirmed the model's prediction that beam confinement and phase matching conditions must be precisely controlled to maximize photon purity and heralding probability.

Robust Quantum Systems Path

This work is promising since it correctly simulates and computes source parameters and estimates the chance of single-photon production following time multiplexing. Photon storage and release are finely controlled in the unique method to maximize single-photon generation efficiency.

OAM orbital angular momentum Twisted light reveals relativistic motion in the universe

Fazilah Nothlawala and her Glasgow University colleagues, along with scientists from the University of the Witwatersrand and Heriot-Watt University, have developed a new method to accurately measure relativistic effects like Lorentz contraction factors by observing the “twist” in entangled light. This innovative idea uses light's fundamentals. By extending orbital angular momentum (OAM) metrology into special relativity, this unique method may be more precise and versatile than existing methods for measuring speeds near the speed of light.

According to Einstein's theory of relativity, light's characteristics change when viewed from a moving perspective. One of the theory's more perplexing predictions is length contraction, which occurs when things appear shorter as their velocity rises. Until previously, measuring these affects directly was impossible, especially under extreme conditions.

The orbital angular momentum (OAM) of light drives this novel technique. OAM describes the helical twist that gives photons their “twist”. Because OAM is not Lorentz invariant, its properties rely on detection speed. This non-invariance makes OAM a sensitive relativistic motion probe. The Quantum Evangelist from one source says quantum mechanics “is a way of understanding the world at its most fundamental level” and “challenges our preconceptions.” This study embodies such spirit.

Researchers used the relationships between entangled photon pairs whose features are naturally related. Entangled photons were created via Spontaneous Parametric Down-Conversion (SPDC), in which a pump laser interacts with a nonlinear crystal to create two new photons. They photographed the crystal's plane with two SLMs.

The primary finding of the study is that length contraction alters OAM spectrum correlations of entangled photons viewed at different speeds. The spatial rescaling caused by relativistic motion changes the orthogonality of OAM waveforms. Consequently, OAM spectrum broadens. As the Lorentz factor grows or speed approaches light speed, the OAM spectrum widens and orthogonality breaks.

The group demonstrated this with a simulation. To simulate relativistic length contraction, they encoded distorted detecting modes with spatial light modulators (SLMs) as "contracted detectors". They calculated the joint probability distribution of the observed OAM modes of the entangled photon pairs to quantify this broadening. The experimental setup confirmed the theoretical predictions, showing a direct link between the expected Lorentz factor and OAM spectrum alterations.

The group mathematically linked the OAM spectrum to the Lorentz factor. They showed that the Lorentz factor may be extracted from OAM measurements' conditional probabilities. For a range of encoded Lorentz factors, from rest frame to empirically measured joint probability spectra, theoretical predictions matched experimental results. This allowed scientists to mimic velocities up to 0.99c (99% of light speed) in the lab and quantitatively derive the Lorentz (contraction) factor.

Due to this work, metrology has evolved greatly. OAM's non-Lorentz invariance and structured light's properties have allowed the researchers to measure precisely in severe conditions. The findings lay the groundwork for relativistic measuring methods.