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The Japan Society of Applied Physics

Spectral correlation measurement in Hong-Ou-Mandel interference between two independent sources

Rui‐Bo Jin, Thomas Gerrits, Mikio Fujiwara, Ryota Wakabayashi, Taro Yamashita, Shigehito Miki, Hirotaka Terai, Ryōsuke Shimizu, Masahiro Takeoka, Masahide Sasaki

Published Feb 8, 2016• 0 citations
OpenAlex

Abstract

Hong-Ou-Mandel interference between independent photon sources (HOMI-IPS) plays an important role in quantum information processing. A variety of HOMI-IPS experiments have been demonstrated at near-infrared wavelengths or telecom wavelengths [1]. In all the previous HOMI-IPS experiments, the HOM dips are obtained by recording the four-fold coincidence counts as a function of the temporal delay. However, the spectral correlation during the interference is omitted, partially due to technical difficulties, e.g., the acquisition time is too long for measuring a joint spectral distribution. Spectral information, as the conjugate of the temporal information in the Fourier transformation, is definitely of great importance and should be investigated. Very recently, a new technique of spectral correlation measurement in a HOM interference has been developed by Gerrits, et al [2]. This technique has the merits of high speed and high resolution, therefore, has been used as a powerful tool to analyse the spectral correlation in a HOM interference between signal and idler photons from one spontaneous parametric down conversion (SPDC) source. In this work, we measure the joint spectral distribution in HOMI-IPS using the new technique developed in [2]. The experimental setup is shown in Fig. 1 (Left). The two independent sources are based on SPDC from two 30-mm-long periodically poled KTiOPO4 (PPKTP) crystals pumped by picosecond laser pulses (76 MHz, 792 nm, temporal duration ~ 2 ps). In Fig. 1 (Left), the dispersion compensation fiber model (DCFMs), the superconducting nanowire single-photon detectors (SNSPDs) [3,4,5] and the time interval analyzer (TIA) constitute a fiber spectral analyzer [6]. Fig. 1(Right: (a)) is the measured four-fold HOM interference between signal1 and signal2, with idler1 and idler2 as heralders. Without subtraction of any background counts, the raw visibility of the HOM dip is 69.9±3.2%, which is consistent with our previous results in [1,7,8]. Fig. 1(Right: (b)-(g)) are the measured joint spectral intensities at different delay positions. The splitting phenomenon in the joint spectral distribution is clearly observed. The experimental results agree well with our theoretical simulations. This experiment not only can deepen our understanding of HOMI-IPS from the viewpoint of spectral domain, but also can be used to improve the visibility of HOMI-IPS by temporal filtering.

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Spectrally resolved Hong-Ou-Mandel interference between independent photon sources

Rui-Bo Jin, Thomas Gerrits, Mikio Fujiwara +7 more

Hong-Ou-Mandel (HOM) interference between independent photon sources (HOMI-IPS) is the fundamental block for quantum information processing. All the previous HOMI-IPS experiments were carried out in time-domain, however, the spectral information during the interference was omitted. Here, we investigate the HOMI-IPS in spectral domain using the recently developed fast fiber spectrometer, and demonstrate the spectral distribution during the HOM interference between two heralded single-photon sources, and two thermal sources. This experiment not only can deepen our understanding of HOMI-IPS from the viewpoint of spectral domain, but also presents a tool to test the theoretical predictions of HOMI-IPS using spectrally engineered sources.

arXiv:1507.02424•Optics Express•Oct 27, 2015•64 citations

High visibility Hong-Ou-Mandel interference via a time-resolved coincidence measurement

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A high visibility Hong-Ou-Mandel (HOM) interference between two independently prepared photons plays an important role in various photonic quantum information processing. In a standard HOM experiment using photons generated by pulse-pumped spontaneous parametric down conversion (SPDC), larger detection time windows than the coherence time of photons have been employed for measuring the HOM visibility and/or drawing the HOM dip. If large amounts of stray photons continuously exist within the detection time windows, employing small detection time windows is favorable for reducing the effect of background noises. Especially, such a setup is helpful for the HOM experiment using continuous wave (cw)-pumped SPDC and the time-resolved coincidence measurement. Here we argue that the method for determining the HOM visibility used in the previous cw experiments tends to suffer from distortion arising from biased contribution of the background noises. We then present a new method with unbiased treatment of the cw backgrounds. By using this method, we experimentally demonstrate a high visibility HOM interference of two heralded telecom photons independently generated by SPDC with employing cw pump light. An observed HOM visibility is 0.87 ± 0.04, which is as high as those observed by using pulse-pumped SPDC photons.

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Entanglement swapping enables the distribution of quantum states over long distances. In this protocol, a Bell state measurement projects photons, which were created in separate entangled photon sources, into an entangled state when their corresponding pairs interfere at a beamsplitter. This process is optimally realized when the photons are indistinguishable in all degrees of freedom, resulting in Hong-Ou-Mandel (HOM) interference. Since its initial proposal by [1], several experimental realizations have used pulsed, synchronized pumps, as in [2] to achieve temporal indistiguishability. In the case of continuous wave (CW) pumping, the sources are not synchronized, requiring post-selection of the coincidence events after detection. This requires detectors with a temporal resolution greater than the coherence time of the photons. Previous experiments have successfully observed HOM interference using periodically poled Lithium Niobate (ppLN) waveguides and superconducting nanowire single-photon detectors (SNSPDs) [3], also with hybrid sources to improve coincidence rates and HOM visibility [4], [5].

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In this work we demonstrate spectral-temporal correlation measurements of the Hong-Ou-Mandel (HOM) interference effect with the use of a spectrometer based on a photon-counting camera. This setup allows us to take, within seconds, spectral temporal correlation measurements on entangled photon sources with sub-nanometer spectral resolution and nanosecond timing resolution. Through post processing, we can observe the HOM behaviour for any number of spectral filters of any shape and width at any wavelength over the observable spectral range. Our setup also offers great versatility in that it is capable of operating at a wide spectral range from the visible to the near infrared and does not require a pulsed pump laser for timing purposes. This work offers the ability to gain large amounts of spectral and temporal information from a HOM interferometer quickly and efficiently and will be a very useful tool for many quantum technology applications and fundamental quantum optics research.

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Hong-Ou-Mandel interference between two independent all-fiber multiplexed photon sources

Li Yin-Hai, Zhao-Huai Xu, Shuang Wang +3 more

Interference between independent photon sources is the key technique to realize complex quantum systems for more sophisticated applications such as multi-photon entanglement generation and quantum teleportation. Here, we report Hong-Ou-Mandel interference (HOMI) between two independent 1.55 m all-fiber photon pair sources over two 100 GHz dense wave division multiplexing (DWDM) channels, whose visibility reaches 53.2%8.4% (82.9%5.3%) without (with) back ground counts subtracted. In addition, we theoretically describe in detail the single photon spectral purity of the photon source generated in dispersion shifted fiber (DSF), simulate the influences of the pulse width and filter bandwidth on the purity, and obtain the optimized condition. The optimized pump pulse width is 8 ps and filter bandwidth is about 40 GHz or less. A home-made 1550.1 nm mode-locked fiber laser source, whose pulse width and repetition rate are 25 ps and 27.9 MHz respectively, acts as a pump of photon source. A tunable attenuator is used to adjust the pump power of the photon source, and the broad band background fluorescence photons are filtered out by cascade 100 GHz DWDM filters. The clean pump beam is divided into two equal parts by the 50 : 50 optical coupler to pump two 300 m DSFs (cooled by liquid nitrogen) to generate independent photon sources. Then the strong pump beam and noise photon from Raman scattering in orthogonal polarization are removed by 2 groups of 200 GHz DWDM filters and fiber polarization rotator and polarizer. Then two 100 GHz DWDMs are used for separating photons at correlated channel pairs. The relative delay between the two independent photons is adjusted by tunable fiber delay line. Photons from the same channels are combined in a second beam splitter for interference, and the other two photons are used as trigger signals. The two triggered photons are detected by two free running InGaAs avalanched single photon detectors (APD1, APD4, ID Quanta, ID220, 20% detection efficiency, 3 s dead time, dark count rate 4k cps), and the outputs of detectors APD1 and APD4 are used to trigger two single-photon detectors running in the gated mode (APD2, APD3, Qasky, Hefei, China, 100 MHz, free gating single photon detectors, 20% detection efficiency, dark count probability 410-5 per gate) for twophoton coincidence measurement. Detection output signals from APD2 and APD3 are sent to our coincidence count device (Pico quanta, TimeHarp 260, 1.6 ns coincidence window) for four-photon coincidence measurement. Before measuring the HOMI, we obtain a maximum-coincidence-to-accidental-coincidence ratio (CAR) of 131 by cooling the fiber in liquid nitrogen when the pump power is 23 W. There are a few remarks we want to point out.Firstly, the photon sources are not operated at the optimized pump pulse width for pure single photon generation, but narrow band 100 GHz filters are used in the experiments to increase the purity of the sources. Secondly, single photon detectors used in our experiment have lower detection efficiency and much higher dark counts than nano-wire single photon detectors, if we have high-performance nano-wire single photon detector, experimental results will be greatly improved due to the four-fold coincidences and dark coincidences scaling quadruplicate with the detection efficiency and dark count probability of a single detector. Thirdly, we use relatively high pump power for each DSF (0.12 mW) to reduce measurement time for photon coincidence, which will lead to a very poor raw visibility certainly. Finally, though only a 100 GHz channel pair is used in our experiment, we can use other channels for multiplexing such interference processes to improve the channel capacity in future quantum communication tasks theoretically. Our study shows greatly promising integrated optical elements for future scalable quantum information processing.

Acta Physica Sinica•Jan 1, 2017•2 citations

Interference of Independent, Telecom Wavelength, Heralded Single Photons from PCF and PPLN Based Sources

R. Mcmillan A., Laurent Labonté, Alex S. Clark +5 more

Heralded single photons with wavelength near 1550nm are expected to be an important resource for future quantum communications applications. Such applications often rely on non-classical Hong Ou Mandel interference (HOMI) that is observed between indistinguishable, pure photon states. While high visibility HOMI is routinely achieved for photons from identically prepared sources, here we observe interference between photons from two dissimilar systems. To generate synchronised indistinguishable photons, two photon sources were pumped with a single 1064nm, picosecond-pulsed fibre laser. In one source the laser pulses generated correlated pairs of photons at 810nm and 1550nm through four-wave mixing in photonic crystal fibre (PCF). In the other, the laser was used to generate second harmonic light at 532nm in a bulk crystal, before being launched into a periodically poled lithium niobate (PPLN) waveguide. This structure was designed to generate signal and idler photons through parametric down-conversion, matched in wavelength to the fibre based source. Idler photons from both sources were input into a fused-fibre coupler in order to measure the HOMI visibility. HOMI with a net visibility of 70% was demonstrated between photons from the two sources (after accounting for the background due to emission of multiple photons from a single source). A visibility of 80% is anticipated for the current sources after further improvement in the purity of the generated states. This result is the first step towards realising a quantum relay system, in which transmitted qubits produced by low loss, fibre-based photon sources interact with photons produced locally on a chip.

•Sep 3, 2012•0 citations
Hong-Ou-Mandel interference between independent photon sources (HOMI-IPS) plays an important role in quantum information processing. A variety of HOMI-IPS experiments have been demonstrated at near-infrared wavelengths or telecom wavelengths [1]. In all the previous HOMI-IPS experiments, the HOM dips are obtained by recording the four-fold coincidence counts as a function of the temporal delay. However, the spectral correlation during the interference is omitted, partially due to technical difficulties, e.g., the acquisition time is too long for measuring a joint spectral distribution. Spectral information, as the conjugate of the temporal information in the Fourier transformation, is definitely of great importance and should be investigated. Very recently, a new technique of spectral correlation measurement in a HOM interference has been developed by Gerrits, et al [2]. This technique has the merits of high speed and high resolution, therefore, has been used as a powerful tool to analyse the spectral correlation in a HOM interference between signal and idler photons from one spontaneous parametric down conversion (SPDC) source. In this work, we measure the joint spectral distribution in HOMI-IPS using the new technique developed in [2]. The experimental setup is shown in Fig. 1 (Left). The two independent sources are based on SPDC from two 30-mm-long periodically poled KTiOPO4 (PPKTP) crystals pumped by picosecond laser pulses (76 MHz, 792 nm, temporal duration ~ 2 ps). In Fig. 1 (Left), the dispersion compensation fiber model (DCFMs), the superconducting nanowire single-photon detectors (SNSPDs) [3,4,5] and the time interval analyzer (TIA) constitute a fiber spectral analyzer [6]. Fig. 1(Right: (a)) is the measured four-fold HOM interference between signal1 and signal2, with idler1 and idler2 as heralders. Without subtraction of any background counts, the raw visibility of the HOM dip is 69.9±3.2%, which is consistent with our previous results in [1,7,8]. Fig. 1(Right: (b)-(g)) are the measured joint spectral intensities at different delay positions. The splitting phenomenon in the joint spectral distribution is clearly observed. The experimental results agree well with our theoretical simulations. This experiment not only can deepen our understanding of HOMI-IPS from the viewpoint of spectral domain, but also can be used to improve the visibility of HOMI-IPS by temporal filtering.
Hong-Ou-Mandel (HOM) interference between independent photon sources (HOMI-IPS) is the fundamental block for quantum information processing. All the previous HOMI-IPS experiments were carried out in time-domain, however, the spectral information during the interference was omitted. Here, we investigate the HOMI-IPS in spectral domain using the recently developed fast fiber spectrometer, and demonstrate the spectral distribution during the HOM interference between two heralded single-photon sources, and two thermal sources. This experiment not only can deepen our understanding of HOMI-IPS from the viewpoint of spectral domain, but also presents a tool to test the theoretical predictions of HOMI-IPS using spectrally engineered sources.
A high visibility Hong-Ou-Mandel (HOM) interference between two independently prepared photons plays an important role in various photonic quantum information processing. In a standard HOM experiment using photons generated by pulse-pumped spontaneous parametric down conversion (SPDC), larger detection time windows than the coherence time of photons have been employed for measuring the HOM visibility and/or drawing the HOM dip. If large amounts of stray photons continuously exist within the detection time windows, employing small detection time windows is favorable for reducing the effect of background noises. Especially, such a setup is helpful for the HOM experiment using continuous wave (cw)-pumped SPDC and the time-resolved coincidence measurement. Here we argue that the method for determining the HOM visibility used in the previous cw experiments tends to suffer from distortion arising from biased contribution of the background noises. We then present a new method with unbiased treatment of the cw backgrounds. By using this method, we experimentally demonstrate a high visibility HOM interference of two heralded telecom photons independently generated by SPDC with employing cw pump light. An observed HOM visibility is 0.87 ± 0.04, which is as high as those observed by using pulse-pumped SPDC photons.
Entanglement swapping enables the distribution of quantum states over long distances. In this protocol, a Bell state measurement projects photons, which were created in separate entangled photon sources, into an entangled state when their corresponding pairs interfere at a beamsplitter. This process is optimally realized when the photons are indistinguishable in all degrees of freedom, resulting in Hong-Ou-Mandel (HOM) interference. Since its initial proposal by [1], several experimental realizations have used pulsed, synchronized pumps, as in [2] to achieve temporal indistiguishability. In the case of continuous wave (CW) pumping, the sources are not synchronized, requiring post-selection of the coincidence events after detection. This requires detectors with a temporal resolution greater than the coherence time of the photons. Previous experiments have successfully observed HOM interference using periodically poled Lithium Niobate (ppLN) waveguides and superconducting nanowire single-photon detectors (SNSPDs) [3], also with hybrid sources to improve coincidence rates and HOM visibility [4], [5].
In this work we demonstrate spectral-temporal correlation measurements of the Hong-Ou-Mandel (HOM) interference effect with the use of a spectrometer based on a photon-counting camera. This setup allows us to take, within seconds, spectral temporal correlation measurements on entangled photon sources with sub-nanometer spectral resolution and nanosecond timing resolution. Through post processing, we can observe the HOM behaviour for any number of spectral filters of any shape and width at any wavelength over the observable spectral range. Our setup also offers great versatility in that it is capable of operating at a wide spectral range from the visible to the near infrared and does not require a pulsed pump laser for timing purposes. This work offers the ability to gain large amounts of spectral and temporal information from a HOM interferometer quickly and efficiently and will be a very useful tool for many quantum technology applications and fundamental quantum optics research.
Interference between independent photon sources is the key technique to realize complex quantum systems for more sophisticated applications such as multi-photon entanglement generation and quantum teleportation. Here, we report Hong-Ou-Mandel interference (HOMI) between two independent 1.55 m all-fiber photon pair sources over two 100 GHz dense wave division multiplexing (DWDM) channels, whose visibility reaches 53.2%8.4% (82.9%5.3%) without (with) back ground counts subtracted. In addition, we theoretically describe in detail the single photon spectral purity of the photon source generated in dispersion shifted fiber (DSF), simulate the influences of the pulse width and filter bandwidth on the purity, and obtain the optimized condition. The optimized pump pulse width is 8 ps and filter bandwidth is about 40 GHz or less. A home-made 1550.1 nm mode-locked fiber laser source, whose pulse width and repetition rate are 25 ps and 27.9 MHz respectively, acts as a pump of photon source. A tunable attenuator is used to adjust the pump power of the photon source, and the broad band background fluorescence photons are filtered out by cascade 100 GHz DWDM filters. The clean pump beam is divided into two equal parts by the 50 : 50 optical coupler to pump two 300 m DSFs (cooled by liquid nitrogen) to generate independent photon sources. Then the strong pump beam and noise photon from Raman scattering in orthogonal polarization are removed by 2 groups of 200 GHz DWDM filters and fiber polarization rotator and polarizer. Then two 100 GHz DWDMs are used for separating photons at correlated channel pairs. The relative delay between the two independent photons is adjusted by tunable fiber delay line. Photons from the same channels are combined in a second beam splitter for interference, and the other two photons are used as trigger signals. The two triggered photons are detected by two free running InGaAs avalanched single photon detectors (APD1, APD4, ID Quanta, ID220, 20% detection efficiency, 3 s dead time, dark count rate 4k cps), and the outputs of detectors APD1 and APD4 are used to trigger two single-photon detectors running in the gated mode (APD2, APD3, Qasky, Hefei, China, 100 MHz, free gating single photon detectors, 20% detection efficiency, dark count probability 410-5 per gate) for twophoton coincidence measurement. Detection output signals from APD2 and APD3 are sent to our coincidence count device (Pico quanta, TimeHarp 260, 1.6 ns coincidence window) for four-photon coincidence measurement. Before measuring the HOMI, we obtain a maximum-coincidence-to-accidental-coincidence ratio (CAR) of 131 by cooling the fiber in liquid nitrogen when the pump power is 23 W. There are a few remarks we want to point out.Firstly, the photon sources are not operated at the optimized pump pulse width for pure single photon generation, but narrow band 100 GHz filters are used in the experiments to increase the purity of the sources. Secondly, single photon detectors used in our experiment have lower detection efficiency and much higher dark counts than nano-wire single photon detectors, if we have high-performance nano-wire single photon detector, experimental results will be greatly improved due to the four-fold coincidences and dark coincidences scaling quadruplicate with the detection efficiency and dark count probability of a single detector. Thirdly, we use relatively high pump power for each DSF (0.12 mW) to reduce measurement time for photon coincidence, which will lead to a very poor raw visibility certainly. Finally, though only a 100 GHz channel pair is used in our experiment, we can use other channels for multiplexing such interference processes to improve the channel capacity in future quantum communication tasks theoretically. Our study shows greatly promising integrated optical elements for future scalable quantum information processing.
Heralded single photons with wavelength near 1550nm are expected to be an important resource for future quantum communications applications. Such applications often rely on non-classical Hong Ou Mandel interference (HOMI) that is observed between indistinguishable, pure photon states. While high visibility HOMI is routinely achieved for photons from identically prepared sources, here we observe interference between photons from two dissimilar systems. To generate synchronised indistinguishable photons, two photon sources were pumped with a single 1064nm, picosecond-pulsed fibre laser. In one source the laser pulses generated correlated pairs of photons at 810nm and 1550nm through four-wave mixing in photonic crystal fibre (PCF). In the other, the laser was used to generate second harmonic light at 532nm in a bulk crystal, before being launched into a periodically poled lithium niobate (PPLN) waveguide. This structure was designed to generate signal and idler photons through parametric down-conversion, matched in wavelength to the fibre based source. Idler photons from both sources were input into a fused-fibre coupler in order to measure the HOMI visibility. HOMI with a net visibility of 70% was demonstrated between photons from the two sources (after accounting for the background due to emission of multiple photons from a single source). A visibility of 80% is anticipated for the current sources after further improvement in the purity of the generated states. This result is the first step towards realising a quantum relay system, in which transmitted qubits produced by low loss, fibre-based photon sources interact with photons produced locally on a chip.