Source of single correlated photons at 1.06-mkm wavelength

Abstract

We describe the source of correlated photon pairs at 1.06 micron wavelength based on spontaneous parametric downconversion. The events corresponding to the photons in the pair are correlated with time accuracy better than 1 ns. Apart from wavelength, another distinctive feature of our set-up is that the "signal" photons can be delayed by passing the additional distance ( up to 10 m) in the air Keywords-quantum optics; down-conversion; single photonSpontaneous parametric down-conversion (SPDC) has ͒ become one of the most reliable technique for generation (to a good approximation) of single photons and correlated, including entangled, photon pairs. Such photon sources are used as a key element in testing of the foundations of quantum mechanics, quantum information and Bell test experiments, in experimental realization of a number of quantum optics technologies such as quantum cryptography. Improvements in down-conversion schemes have led to a considerable improvement of the quality of such sources.Nowadays different type of lasers are used as a pump for SPDC process in nonlinear crystal: GaN lasers (405 nm), HeCd ͒ (441.6nm), different lines of Argon-ion lasers. To our knowledge, the attempts of using lasers with 0.532 mkm wavelength are extremely rare. It seems to be associated with more complex experimental realization of such schemes and, last but not least, with a lower quantum yield and a higher price of single-photon counters at a wavelength of 1.064 mkm. However, such sources may be useful in applications where the further amplification of single photons are needed. Having our source the Nd:YAG lasers can be used, which are among the most reliable lasers currently used in industry.In this report we present the description and characterize the source of single correlated photons at 1.06 mkm wavelength based on BBO parametric down-covertion crystal pumped by 0.532-mkm SHG radiation of cw diode-pumped YAG:Nd 3+ laser. The power of the laser can be varied from 5 to 300 mW. We used 3-mm BBO crystal cut for noncollinear (±3 o ) type-I SPDC. For detection of photon pairs we used the cooled single-photon detectors optimized for 1064nm from ID Quantique (id400 SERIES) and an 8-channel time-to-digital converter (IDQ's id800-TDC) for registering exact times of incoming signal events from single-photon detectors. Recorded far-field spatial distributions of the SPDC light for various ͒ tuning angles of the crystal are shown in Fig.1. Images demonstrate quality of the SPDC scheme operation in 1.06 ͒ mkm spectral range. Stable correlation was observed at all delays between the signal and idler photons. Typical histogram is shown in Figure 2. For each photon detected at the moment t1 in channel 1 we found nearest previous and nearest next photons, detected either in channel 1 or in channel 2. If nearest photon is detected in channel 2 at the time t2, we added an event with delay value t1 -t2 to the histogram. The same operation is made for photons detected on channel 2. The results were organized as the histogram of time d...