Single Photon State

M. Bertolotti

Anjali Jatwani, Amit Verma

A single-photon source is a key advancement for quantum computing, quantum sensing, metrology, and quantum communication. These applications use single photons and have demanding standards for the effectiveness of single-photon generation. All available single photon source (SPS) is probabilistic and the search for deterministic SPS is challenging and relatively new. In this work, we explore a quantitative approach that can be applied to various sources with well-defined mathematical distribution functions in photon emission. If we have a photon number distribution, then we can easily compute the possibility of emission of a single photon from the source. Here, we observe the single photon possibility in a quantum state named as New Generalised Binomial State. Furthermore, this criterion has been applied to a single photon added New Generalised Binomial state and a single photon subtracted New Generalised Binomial State too. This technique helps us to characterize the quality of a single photon source. We explore the variation of SPS probability with different parameters and it is found that probability varies with the total number of photons in a system, the q parameter should be negative and the addition of a Photon is more suitable than subtraction for single photon source criterion.

David Gevaux

Tao Hong, Michael W. Jack, Makoto Yamashita

We propose a method for producing on-demand single-photon states based on collision-induced exchanges of photons and unbalanced linear absorption between two single-mode light fields. These two effects result in an effective nonlinear absorption of photons in one of the modes, which can lead to single-photon states. A quantum nonlinear attenuator based on such a mechanism can absorb photons in a normal input light pulse and terminate the absorption at a single-photon state. Because the output light pulses containing single photons preserve the properties of the input pulses, we expect this method to be a means for building a highly controllable single-photon source.

Shengwang Du

M. A. A. Rahim, Mohd Amir Radhi Othman

Single-photon sources that emit only one photon at a time with high yield are important for security and efficiency in quantum communication and computation, respectively. One method to develop the desired single-photon source is through entangled single-photon pairs from spontaneous parametric down-conversion (SPDC) crystals where detection of idler photons “heralds” the presence of signal photons. If the SPDC crystal is pumped with weak intensity laser, high purity heralded single photons can be produced at the cost of low yield. Increasing the yield by using stronger laser intensity inevitably decreases the purity due to the presence of multiple photons. Here, we propose a conceptual method to overcome this trade-off between single-photon purity and single-photon yield. Our setup consists of a weakly pumped SPDC crystal seeded with strong coherent states (CS) at the idler mode. Clicks on a click detector at the idler mode conditionally prepare a superposition state of zero-, one-, and two-photon Fock states (FS) at the signal mode. By employing repeated processes of infinitesimal displacement (ID) and two-photon elimination (PE), we can obtain a final state of one-photon FS. Based on the heralding probability (single-photon yield) and single-photon fidelity (single-photon purity), we found that our method transforms the initial state with high heralding probability but low single-photon fidelity (near minimum) to a final state with high heralding probability and high single-photon fidelity (maximum). Furthermore, we discussed the conditions required for the experimental implementations of the processes. Thus, our work paves the way to producing heralded single photons with high purity and yield in SPDC sources.