The Power of Entanglement
Entanglement is as wondrous as it is useful. It describes systems where—counter to our everyday intuition of probability—the full state cannot be described as a product of its constituents, and the measurement of one portion of an entangled ensemble will affect the other parts instantaneously, regardless of the separation in space and time. Together with the interference of coherently prepared quantum amplitudes, it gives rise to the strange and wonderful pantheon of quantum phenomena.
In a series of recent research projects, great strides have been made towards practical and scalable high performance photonic entanglement sources and their exploitation in material characterization.
The entanglement sources developed and used in the three referenced works are based around spontaneous parametric down conversion (SPDC), albeit in various designs, configurations and material systems. In general, to characterize the performance of such devices, the key figures-of-merit to measure include:
- Pair Coincidence Rate (PCR): The rate at which photon pairs are generated in the device
- Brightness: How the PCR varies with the incoming pump power
- Coincidence-to-Accidental Ratio (CAR): A measure of spurious multi-photon emissions present in the output
- g(2)(0), the zero-delay second-order autocorrelation: Standard measure for the purity of a single-photon signal
Each of these metrics requires time-correlated single-photon counting (TCSPC) to measure, that is they have a need for single-photon detectors and time controller electronics. These measurements are all improved by having a higher detector efficiency, fewer detector dark counts, and a high degree of timing resolution. However, the most critical measurement is often the g(2)(0) parameter.
To meet the needs of the researchers, ID Quantique provided an array of ID281 superconducting nanowire single-photon detectors. The high efficiency (> 85% at 1550 nm), the high timing precision (< 45 ps FWHM timing jitter) and low detector noise (< 100 Hz dark counts) allowed for the successful characterization of their entanglement sources, the configured two-photon states, and the execution of their quantum-enhanced metrology experiment for fibre core/cladding refractive index differences.
To request more information or a quotation for any ID Quantique products, contact IL Photonics.