Four-photon quantum interferometry at a telecom wavelength

Abstract

We report the experimental demonstration of four-photon quantum interference using telecomwavelength photons. Realization of multi-photon quantum interference is essential to linear optics quantum information processing and measurement-based quantum computing. We have developed a source that efficiently emits photon pairs in a pure spectrotemporal mode at a telecom wavelength region, and have demonstrated the quantum interference exhibiting the reduced fringe intervals that correspond to the reduced de Broglie wavelength of up to the four photon 'NOON' state. Our result should open a path to practical quantum information processing using telecom-wavelength photons.A variety of novel quantum optical technologies have been proposed for use in quantum information processing and quantum metrology [1,2]. Photons are the most promising and practical media to demonstrate such novel quantum technologies. Indeed, linear optical quantum computing [3] and measurement-based quantum computing [4] have attracted much attention. However, use of the latest quantum technologies requires a large number of multiple photons at the same time. Furthermore, the photons must be indistinguishable from each other because the quantum operations rely on quantum interference between photons. Thus, we need practical and efficient sources that can provide many, indistinguishable photons. To date, quantum processing including up to six photons has been demonstrated [5,6]. These demonstrations used near infrared (800-nm band) photons, for which efficient photon sources and reliable single-photon detectors are available. However, use of telecom-band (1.5-µm band) photons is desired for practical purposes.Here we report an experiment with four-photon quantum interference using telecom-wavelength photons, in which the photons exhibited reduced (∝ N −1 ) fringe intervals corresponding to the number (N ) of photons [7][8][9][10][11][12][13]. Combined with the recent developments of novel photon-detecting devices [14], our result should open a path to practical quantum information processing using telecom-wavelength photons.The most popular photon sources so far used for the demonstration of quantum information processing are based on spontaneous parametric down-conversion (SPDC), which generates twin (signal and idler) photons that can be used as entangled photons [15] or heralded single photons [16]. The linear optical quantum computing [3] and measurement-based quantum computing [4] both rely on quantum interference between photons to carry out quantum operations and quantum measurements. Photons generated by SPDC must be indistinguishable from each other to make them interfere. To do so, spectrotemporal purity of the photons is essential [17]. However, in general, photons generated by SPDC have spectrotemporal correlation [18] that destroys the purity of each photon. Spectral filtering has often been used to purify the spectrotemporal modes of photons; however, such filtering inevitably reduces the generation efficiency. Thus, efficient generation...

Efficient detection of an ultra-bright single-photon source using superconducting nanowire single-photon detectors

“…4(a), where the probabilities of multi-pair components increase rapidly as pump power increases. These multi-pair components at high pump power are useful for multi-photon entangled state generation [32] or multi-photon interferometry [16] from a single SPDC source at telecom wavelengths.…”

“…For example, in Refs [12][13][14][15][16][17][18], the photons were detected by InGaAs APDs with less than or equal to 25% quantum efficiency; and in Refs [12,16], to match the low speed of the InGaAs APDs, the repetition rate of the pump laser was decreased from 76 MHz to around 4 MHz, so the performance of this source was not fully demonstrated. Therefore, the second motivation of this experiment is to fully characterize the performance this highly efficient single-photon source.…”

“…In all the previous experiments [12][13][14][15][16][17][18][19][20][21][22], however, this highly efficient photon source was detected by lowefficiency or low-speed detectors. For example, in Refs [12][13][14][15][16][17][18], the photons were detected by InGaAs APDs with less than or equal to 25% quantum efficiency; and in Refs [12,16], to match the low speed of the InGaAs APDs, the repetition rate of the pump laser was decreased from 76 MHz to around 4 MHz, so the performance of this source was not fully demonstrated.…”

“…From the perspective of single-photon sources, the one based on a spontaneous parametric down-conversion (SPDC) process from a periodically poled KTiOPO 4 (PPKTP) crystal has been proved to be very promising in many experiments [12][13][14][15][16][17][18][19][20][21][22][23]. The PPKTP crystal has a high nonlinear efficiency and a high damage threshold.…”

Pulsed source of spectrally uncorrelated and indistinguishable photons at telecom wavelengths

“…This approach has been implemented in various media such as bulk crystals [12][13][14], waveguides [15,16], or fibers [17]. Quantum communication requires narrowband sources and recent focus has shifted to using periodically poled potassium titanyl phosphate (PPKTP) nonlinear crystals with ps pulsed lasers [18][19][20][21][22][23] to address these demands of quantum communication. We have combined this approach with some of our recent work on optimising source-to-fibre coupling [24] to realise multi-photon experiments with pure, indistinguishable narrowband telecom photons with high levels of purity and coupling efficiencies that are ideally suited to testing quantum network protocols.…”