A multi-functional superconductor single-photon detector at telecommunication wavelength

Abstract A multi-functional single-photon detector wasdemonstrated to resolve photon states by multiple supercon-ductorsinglephotondetectors(SSPDs)systemwithimprovedreadout settings. The photon number and space distributionwereresolvedsimultaneously bythe presented system, whichinheritsthemeritsofSSPD,suchaswide-responseband,highrepetition rate and working stability. Experimentally, fourphotons were resolved and the photon distribution over threepixels was figured out according to the amplitudes of outputpulsesatthetelecommunicationwavelength.Theextensionofthisproposaltoincorporatemoreelementsforresolvingmorephotons and revealing photons spatial distribution over largerscale is also discussed.1 IntroductionPhotonic quantum states can be characterized by theamplitude and phase for higher photon numbers, and by thephoton number distribution for low photon numbers. In thelatter case, measurements are always taken using a single-photon detector (SPD). Most SPDs are binary systems thatdo not take account of photon number, wavelength, phaseor position. SPDs with more functions for revealing thestates of photons are significant in the applications ofquantum physics, such as quantum radar [1], quantumcomputing [2] and quantum communication. For instance,SPDs capable of resolving photon number may improve thesecurity of practical quantum key distribution (QKD) [3].SPDs are also expected to produce the information of time,space and intensity of photons in the applications ofmolecular luminescence imaging and lifetime measure-ment [4–6]. The SPDs with functions to resolve manyquantum states directly can be called as multi-functionalSPDs, which is of great concern for both fundamentalresearch and practical applications, especially in infraredwavelength.Superconductor single photon detector (SSPD) is a newsingle-photon detector developed in recent decade [7]. It isa promising candidate in many applications for wide-response band, low-noise and high-repetition rate. Buttraditional SSPDs are also binary detectors. Multi-elementSSPDs were first introduced to resolve photon in experi-ment [8, 9]. Many attempts [10–18] have been made toresolve photon number by parallel or series connectedniobium nitride nanowires. But it is a challenging work togive more information of incident photons, such as thespace information, wavelength and polarization statesimultaneously for SSPDs.For revealing more information of incident photons, weproposed a multi-functional system based on SSPDs com-bined with RF combiners without exciting instability asparallel or series connected niobium nitride nanowires chips[15]. The demonstrated system is capable of registeringincident photons, resolving photon number and spatial dis-tribution simultaneously by the amplitude of output pulses.At the same time, this system is simple in structure andworking stable and inherits the merit of SSPDs.