## Observation of two output light pulses from a partial wavelength converter preserving phase of an input light at a single-photon level |

Optics Express, Vol. 21, Issue 23, pp. 27865-27872 (2013)

http://dx.doi.org/10.1364/OE.21.027865

Acrobat PDF (903 KB)

### Abstract

We experimentally demonstrate that both of the two output light pulses of different wavelengths from a wavelength converter with various branching ratios preserve phase information of an input light at a single-photon level. In our experiment, we converted temporally-separated two coherent light pulses with average photon numbers of ∼ 0.1 at 780 nm to light pulses at 1522 nm by using difference-frequency generation in a periodically-poled lithium niobate waveguide. We observed an interference between temporally-separated two modes for both the converted and the unconverted light pulses at various values of the conversion efficiency. We observed interference visibilities greater than 0.88 without suppressing the background noises for any value of the conversion efficiency the wavelength converter achieves. At a conversion efficiency of ∼ 0.5, the observed visibilities are 0.98 for the unconverted light and 0.99 for the converted light. Such a phase-preserving wavelength converter with high visibilities will be useful for manipulating quantum states encoded in the frequency degrees of freedom.

© 2013 OSA

## 1. Introduction

1. P. Kumar, “Quantum frequency conversion,” Opt. Lett. **15**, 1476–1478 (1990). [CrossRef] [PubMed]

2. C. Langrock, E. Diamanti, R. V. Roussev, Y. Yamamoto, M. M. Fejer, and H. Takesue, “Highly efficient single-photon detection at communication wavelengths by use of upconversion in reverse-proton-exchanged periodically poled LiNbO3 waveguides,” Opt. Lett. **30**, 1725–1727 (2005). [CrossRef] [PubMed]

3. M. T. Rakher, L. Ma, O. Slattery, X. Tang, and K. Srinivasan, “Quantum transduction of telecommunications-band single photons from a quantum dot by frequency upconversion,” Nat. Photonics **4**, 786–791 (2010). [CrossRef]

4. H. Takesue, “Erasing Distinguishability Using Quantum Frequency Up-Conversion,” Phys. Rev. Lett. **101**, 173901 (2008). [CrossRef] [PubMed]

5. S. Tanzilli, W. Tittel, M. Halder, O. Alibart, P. Baldi, N. Gisin, and H. Zbinden, “A photonic quantum information interface,” Nature **437**, 116–120 (2005). [CrossRef] [PubMed]

10. R. Ikuta, T. Kobayashi, H. Kato, S. Miki, T. Yamashita, H. Terai, M. Fujiwara, T. Yamamoto, M. Koashi, M. Sasaki, Z. Wang, and N. Imoto, “Nonclassical two-photon interference between independent telecommunication light pulses converted by difference-frequency generation,” Phys. Rev. A **88**, 042317 (2013). [CrossRef]

11. M. Raymer, S. van Enk, C. McKinstrie, and H. McGuinness, “Interference of two photons of different color,” Opt. Commun. **283**, 747–752 (2010). [CrossRef]

12. H. Takesue, “Single-photon frequency down-conversion experiment,” Phys. Rev. A **82**, 013833 (2010). [CrossRef]

13. N. Curtz, R. Thew, C. Simon, N. Gisin, and H. Zbinden, “Coherent frequency-down-conversion interface for quantum repeaters,” Opt. Express **18**, 22099–22104 (2010). [CrossRef] [PubMed]

5. S. Tanzilli, W. Tittel, M. Halder, O. Alibart, P. Baldi, N. Gisin, and H. Zbinden, “A photonic quantum information interface,” Nature **437**, 116–120 (2005). [CrossRef] [PubMed]

7. R. Ikuta, Y. Kusaka, T. Kitano, H. Kato, T. Yamamoto, M. Koashi, and N. Imoto, “Wide-band quantum interface for visible-to-telecommunication wavelength conversion,” Nat. Commun. **2**, 1544 (2011). [CrossRef] [PubMed]

14. S. Ramelow, a. Fedrizzi, a. Poppe, N. Langford, and a. Zeilinger, “Polarization-entanglement-conserving frequency conversion of photons,” Phys. Rev. A **85**, 013845 (2012). [CrossRef]

*et. al.*[15

15. G. Giorgi, P. Mataloni, and F. De Martini, “Frequency hopping in quantum interferometry: Efficient up-down conversion for qubits and ebits,” Phys. Rev. Lett. **90**, 027902 (2003). [CrossRef] [PubMed]

16. S. Zaske, A. Lenhard, and C. Becher, “Efficient frequency downconversion at the single photon level from the red spectral range to the telecommunications C-band,” Opt. Express **19**, 12825–12836 (2011). [CrossRef] [PubMed]

17. L. Ma, O. Slattery, and X. Tang, “Single photon frequency up-conversion and its applications,” Phys. Rep. **521**, 69–94 (2012). [CrossRef]

## 2. Theory of an ideal wavelength conversion

1. P. Kumar, “Quantum frequency conversion,” Opt. Lett. **15**, 1476–1478 (1990). [CrossRef] [PubMed]

7. R. Ikuta, Y. Kusaka, T. Kitano, H. Kato, T. Yamamoto, M. Koashi, and N. Imoto, “Wide-band quantum interface for visible-to-telecommunication wavelength conversion,” Nat. Commun. **2**, 1544 (2011). [CrossRef] [PubMed]

*ω*

_{s}and a converted mode at angular frequency

*ω*

_{c}satisfies

*ω*

_{c}=

*ω*

_{s}−

*ω*

_{p}, where

*ω*

_{p}is the angular frequency of the pump light. When the pump light is sufficiently strong, the effective Hamiltonian of the DFG process is described by where

*â*

_{s}and

*â*

_{c}are annihilation operators of the signal mode and the converted mode, respectively. Here

*ξ*= |

*ξ*|

*e*is proportional to the complex amplitude of the classical pump light. By using Eq. (1), annihilation operators

^{iϕ}*â*

_{s,out}and

*â*

_{c,out}of the signal and converted modes from the nonlinear optical medium are described by and where

*τ*is the propagation time of the pulses through the nonlinear optical medium. Eqs. (2) and (3) are equivalent to the relation between input and output modes of a BS. The transmittance and the reflectance are |cos(

*ξτ*)|

^{2}and |sin(

*ξτ*)|

^{2}, respectively. These can be adjusted by changing the pump power for the wavelength conversion. From Eqs. (2) and (3), the converted light and the remaining unconverted light take over the phase information from the input signal light. In the experiments in [5

5. S. Tanzilli, W. Tittel, M. Halder, O. Alibart, P. Baldi, N. Gisin, and H. Zbinden, “A photonic quantum information interface,” Nature **437**, 116–120 (2005). [CrossRef] [PubMed]

7. R. Ikuta, Y. Kusaka, T. Kitano, H. Kato, T. Yamamoto, M. Koashi, and N. Imoto, “Wide-band quantum interface for visible-to-telecommunication wavelength conversion,” Nat. Commun. **2**, 1544 (2011). [CrossRef] [PubMed]

12. H. Takesue, “Single-photon frequency down-conversion experiment,” Phys. Rev. A **82**, 013833 (2010). [CrossRef]

14. S. Ramelow, a. Fedrizzi, a. Poppe, N. Langford, and a. Zeilinger, “Polarization-entanglement-conserving frequency conversion of photons,” Phys. Rev. A **85**, 013845 (2012). [CrossRef]

15. G. Giorgi, P. Mataloni, and F. De Martini, “Frequency hopping in quantum interferometry: Efficient up-down conversion for qubits and ebits,” Phys. Rev. Lett. **90**, 027902 (2003). [CrossRef] [PubMed]

## 3. Experiment

### 3.1. Experimental setup

_{V}) with a bandwidth of 0.2 nm, an average photon number of each of the temporally-separated light pulses is set to |

*α*|

^{2}, which can be varied from 10

^{−3}to 1 by a variable attenuator (VA). Then the light pulses are coupled to the quasi-phase-matched PPLN waveguide [18

18. T. Nishikawa, A. Ozawa, Y. Nishida, M. Asobe, F.-L. Hong, and T. W. Hänsch, “Efficient 494 mW sum-frequency generation of sodium resonance radiation at 589 nm by using a periodically poled Zn:LiNbO3 ridge waveguide,” Opt. Express **17**, 17792–17800 (2009). [CrossRef] [PubMed]

_{V}, while the light pulses at 1522 nm are diffracted by BG

_{T}with a bandwidth of 1 nm. The temporally-separated two light pulses at each wavelength are divided into a short path (S2) and a long path (L2) with a time difference of 600 ps. After the polarization of the light passing through S2 is flipped, the light pulses from S2 and L2 are mixed by a PBS. Finally, the light pulses are projected onto +45° polarization, and then coupled to single-mode fibers followed by superconducting single-photon detectors (SSPDs) [19

19. S. Miki, M. Takeda, M. Fujiwara, M. Sasaki, and Z. Wang, “Compactly packaged superconducting nanowire single-photon detector with an optical cavity for multichannel system,” Opt. Express **17**, 23557–23564 (2009). [CrossRef]

20. S. Miki, T. Yamashita, M. Fujiwara, M. Sasaki, and Z. Wang, “Multichannel SNSPD system with high detection efficiency at telecommunication wavelength,” Opt. Lett. **35**, 2133–2135 (2010). [CrossRef] [PubMed]

_{V}for the light at 780 nm and D

_{T}for the light at 1522 nm.

_{V}and D

_{T}are connected to a time-to-digital converter (TDC) which is gated by a 1-MHz clock signal. The clock signal is obtained by frequency division of the 82 MHz clock signal from Ti:S laser. There are three possible arrival times in the electric signals from D

_{V}and D

_{T}. The earlest and the latest signals are obtained by the light passing through S1–S2 and L1–L2 paths, respectively. We post-select the 200-ps time windows of the central peaks originated with the light pulses passing through S1–L2 and L1–S2. Such post-selected signals from D

_{V}and D

_{T}should show the first-order interference pattern of the coherent light pulses at 780 nm and 1522 nm, respectively, depending on the position of M.

### 3.2. Experimental results

*α*|

^{2}to ∼ 0.1. The experimental result is shown in Fig. 2(a). From the result, the maximum conversion efficiency is achieved at the pump power of ≈ 560 mW which is smaller than the maximum pump power of 700 mW we can supply. We roughly estimate the internal conversion efficiency in the PPLN crystal as follows. The transmittance of the optical circuit before the wavelength conversion including the coupling efficiency to the PPLN is represented by

*T*

_{in}. The conversion efficiency and the probability of the unconverted events are represented by

*R*(

*P*) and 1 −

*R*(

*P*) =

*T*(

*P*), respectively, where

*P*is the pump power. Note that

*R*(

*P*) corresponds to |sin(

*ξτ*)|

^{2}in Eqs. (2) and (3). We denote overall transmittance of the optical circuit including the quantum efficiency of the detector after the conversion process by

*T*

_{V}for the unconverted light at 780 nm. The detection counts of the unconverted light pulse is described by

*C*=

*𝒩T*

_{in}

*T*(

*P*)

*T*

_{V}, where

*𝒩*is the total number of the input photons. We assume that

*T*

_{in}and

*T*

_{V}take constant values regardless of the pump power. By using

*T*(0mW) = 1 and the observed count of

*C*

_{0}=

*𝒩T*

_{in}

*T*

_{V}at

*P*= 0 mW, we obtain the dependency of

*C/C*

_{0}=

*T*(

*P*) on the pump power as shown in Fig. 2(b). The best fit to

*T*(

*P*) with

*A*≈ 0.94 and

*η*≈ 0.0044/mW.

*T*

_{T}for the converted light at 1522 nm, the detection counts of the converted light is given by

*𝒩T*

_{in}

*R*(

*P*)

*T*

_{T}. Because

*𝒩T*

_{in}

*R*(

*P*)

*T*

_{T}/

*C*

_{0}=

*R*(

*P*)

*T*

_{T}/

*T*

_{V}and

*R*(

*P*) = 1 −

*T*(

*P*),

*T*

_{T}/

*T*

_{V}is estimated from the observed photon count of the unconverted light and that of the converted light at each pump power, which is shown in Fig. 2(b). We see that

*T*

_{T}/

*T*

_{V}takes an almost constant value of about 1.5, which is in accord with the assumption of

*T*

_{V}being constant in our rough estimation.

*α*|

^{2}≈ 0.1. By moving mirror M in Fig. 1, the time difference between the light pulses passing through S1 and L1 is varied. As a result, the first-order interference fringe is observed after mixing the light pulses passing through the paths of S1–L2 and L1–S2. Fig. 3(a) shows the experimental result of the interference fringe when the pump power is 165 mW. For both the unconverted and the converted light pulses, the interference fringes are clearly observed. We define the interference visibility by

*V*= (

*N*

_{max}−

*N*

_{min})/(

*N*

_{max}+

*N*

_{min}), where

*N*

_{max}and

*N*

_{min}are the maximum and the minimum of the count rates, respectively. The observed values of the visibilities are

*V*= 0.98 for the unconverted light and

*V*= 0.99 for the converted light. The standard deviations of the visibilities with the assumption of the Poisson statistics of the counts are less than 0.01. We then measured the visibilities of the interference for various values of the pump power ranging from 0mW to 700mW. The experimental results are shown in Fig. 3(b). For both the converted and the unconverted light pulses, we observed visibilities higher than 0.88.

**2**, 1544 (2011). [CrossRef] [PubMed]

16. S. Zaske, A. Lenhard, and C. Becher, “Efficient frequency downconversion at the single photon level from the red spectral range to the telecommunications C-band,” Opt. Express **19**, 12825–12836 (2011). [CrossRef] [PubMed]

2. C. Langrock, E. Diamanti, R. V. Roussev, Y. Yamamoto, M. M. Fejer, and H. Takesue, “Highly efficient single-photon detection at communication wavelengths by use of upconversion in reverse-proton-exchanged periodically poled LiNbO3 waveguides,” Opt. Lett. **30**, 1725–1727 (2005). [CrossRef] [PubMed]

17. L. Ma, O. Slattery, and X. Tang, “Single photon frequency up-conversion and its applications,” Phys. Rep. **521**, 69–94 (2012). [CrossRef]

21. J. S. Pelc, L. Ma, C. R. Phillips, Q. Zhang, C. Langrock, O. Slattery, X. Tang, and M. M. Fejer, “Long-wavelength-pumped upconversion single-photon detector at 1550 nm : performance and noise analysis,” Opt. Express **19**, 21445–21456 (2011). [CrossRef] [PubMed]

*α*|

^{2}with the fixed pump power of 165 mW. The observed values of

*V*are shown in Fig. 5(a). The high visibilities over 0.9 remain for the converted and the unconverted light pulses for |

*α*|

^{2}> 0.01. The behavior of the visibilities in Fig. 5(a) can be explained by using temporally continuous background noises depending on |

*α*|

^{2}, which was separately measured and is shown in Fig. 5(b). We assume the noise photons are statistically independent of the signal photon counts. Due to the estimated values of the visibilities close to 1 when we subtracted the background noises from the experimental result in Fig. 4(b), we construct a simple model of the visibilities described by the signal photons with unit visibility and the noise photons. In this model, the visibility is given by

*V*= |

*α*|

^{2}

*T*

_{all}

*f*/(|

*α*|

^{2}

*T*

_{all}

*f*+ 2

*d*), where

*T*

_{all}is the overall transmittance of the optical circuit described by

*T*

_{in}

*T*(

*P*)

*T*

_{V}for the unconverted mode and by

*T*

_{in}

*R*(

*P*)

*T*

_{T}for the converted mode. We roughly estimate

*T*

_{in}

*T*

_{V}≈ 0.03 for the unconverted mode and

*T*

_{in}

*T*

_{T}≈ 0.04 for the converted mode from the observed values. From Fig. 2(b), we see

*R*(165mW) =

*T*(165mW) = 0.5.

*f*= 1 MHz is the frequency of the clock and

*d*is the rate of the noise photons. By using polynomial functions fitted to the experimental result of the rates of the noise photons for

*d*as shown in Fig. 5(b), we obtain the expected curves of the visibilities shown in Fig. 5(a), which are in good agreement with the experimental data. From the high visibilities for |

*α*|

^{2}much smaller than 1, the phase-preserving property of the wavelength converter will be expected to hold in a quantum regime. We note that the noise-photon rates take almost constant values for |

*α*|

^{2}< 0.01. These values are the intrinsic optical noises generated through the DFG. On the other hand, for larger values of |

*α*|

^{2}, the noise-count rates increase. We guess this increase may come from the imperfection in the signal light from the Ti:S laser. Because the residual fundamental cw component of the laser is frequency-converted continuously, the effect of the cw component contributes to the constant background photon counts.

## 4. Conclusion

## Acknowledgments

## References and links

1. | P. Kumar, “Quantum frequency conversion,” Opt. Lett. |

2. | C. Langrock, E. Diamanti, R. V. Roussev, Y. Yamamoto, M. M. Fejer, and H. Takesue, “Highly efficient single-photon detection at communication wavelengths by use of upconversion in reverse-proton-exchanged periodically poled LiNbO3 waveguides,” Opt. Lett. |

3. | M. T. Rakher, L. Ma, O. Slattery, X. Tang, and K. Srinivasan, “Quantum transduction of telecommunications-band single photons from a quantum dot by frequency upconversion,” Nat. Photonics |

4. | H. Takesue, “Erasing Distinguishability Using Quantum Frequency Up-Conversion,” Phys. Rev. Lett. |

5. | S. Tanzilli, W. Tittel, M. Halder, O. Alibart, P. Baldi, N. Gisin, and H. Zbinden, “A photonic quantum information interface,” Nature |

6. | Y. Dudin, A. Radnaev, R. Zhao, J. Blumoff, T. Kennedy, and A. Kuzmich, “Entanglement of Light-Shift Compensated Atomic Spin Waves with Telecom Light,” Phys. Rev. Lett. |

7. | R. Ikuta, Y. Kusaka, T. Kitano, H. Kato, T. Yamamoto, M. Koashi, and N. Imoto, “Wide-band quantum interface for visible-to-telecommunication wavelength conversion,” Nat. Commun. |

8. | S. Zaske, A. Lenhard, C. Keßler, J. Kettler, C. Hepp, C. Arend, R. Albrecht, W.-M. Schulz, M. Jetter, P. Michler, and C. Becher, “Visible-to-Telecom Quantum Frequency Conversion of Light from a Single Quantum Emitter,” Phys. Rev. Lett. |

9. | R. Ikuta, H. Kato, Y. Kusaka, S. Miki, T. Yamashita, H. Terai, M. Fujiwara, T. Yamamoto, M. Koashi, M. Sasaki, Z. Wang, and N. Imoto, “High-fidelity conversion of photonic quantum information to telecommunication wavelength with superconducting single-photon detectors,” Phys. Rev. A |

10. | R. Ikuta, T. Kobayashi, H. Kato, S. Miki, T. Yamashita, H. Terai, M. Fujiwara, T. Yamamoto, M. Koashi, M. Sasaki, Z. Wang, and N. Imoto, “Nonclassical two-photon interference between independent telecommunication light pulses converted by difference-frequency generation,” Phys. Rev. A |

11. | M. Raymer, S. van Enk, C. McKinstrie, and H. McGuinness, “Interference of two photons of different color,” Opt. Commun. |

12. | H. Takesue, “Single-photon frequency down-conversion experiment,” Phys. Rev. A |

13. | N. Curtz, R. Thew, C. Simon, N. Gisin, and H. Zbinden, “Coherent frequency-down-conversion interface for quantum repeaters,” Opt. Express |

14. | S. Ramelow, a. Fedrizzi, a. Poppe, N. Langford, and a. Zeilinger, “Polarization-entanglement-conserving frequency conversion of photons,” Phys. Rev. A |

15. | G. Giorgi, P. Mataloni, and F. De Martini, “Frequency hopping in quantum interferometry: Efficient up-down conversion for qubits and ebits,” Phys. Rev. Lett. |

16. | S. Zaske, A. Lenhard, and C. Becher, “Efficient frequency downconversion at the single photon level from the red spectral range to the telecommunications C-band,” Opt. Express |

17. | L. Ma, O. Slattery, and X. Tang, “Single photon frequency up-conversion and its applications,” Phys. Rep. |

18. | T. Nishikawa, A. Ozawa, Y. Nishida, M. Asobe, F.-L. Hong, and T. W. Hänsch, “Efficient 494 mW sum-frequency generation of sodium resonance radiation at 589 nm by using a periodically poled Zn:LiNbO3 ridge waveguide,” Opt. Express |

19. | S. Miki, M. Takeda, M. Fujiwara, M. Sasaki, and Z. Wang, “Compactly packaged superconducting nanowire single-photon detector with an optical cavity for multichannel system,” Opt. Express |

20. | S. Miki, T. Yamashita, M. Fujiwara, M. Sasaki, and Z. Wang, “Multichannel SNSPD system with high detection efficiency at telecommunication wavelength,” Opt. Lett. |

21. | J. S. Pelc, L. Ma, C. R. Phillips, Q. Zhang, C. Langrock, O. Slattery, X. Tang, and M. M. Fejer, “Long-wavelength-pumped upconversion single-photon detector at 1550 nm : performance and noise analysis,” Opt. Express |

**OCIS Codes**

(270.1670) Quantum optics : Coherent optical effects

(190.4223) Nonlinear optics : Nonlinear wave mixing

(270.5565) Quantum optics : Quantum communications

(270.5585) Quantum optics : Quantum information and processing

(130.7405) Integrated optics : Wavelength conversion devices

**ToC Category:**

Quantum Optics

**History**

Original Manuscript: September 12, 2013

Revised Manuscript: October 27, 2013

Manuscript Accepted: October 28, 2013

Published: November 6, 2013

**Citation**

Rikizo Ikuta, Toshiki Kobayashi, Hiroshi Kato, Shigehito Miki, Taro Yamashita, Hirotaka Terai, Mikio Fujiwara, Takashi Yamamoto, Masahide Sasaki, Zhen Wang, Masato Koashi, and Nobuyuki Imoto, "Observation of two output light pulses from a partial wavelength converter preserving phase of an input light at a single-photon level," Opt. Express **21**, 27865-27872 (2013)

http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-23-27865

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### References

- P. Kumar, “Quantum frequency conversion,” Opt. Lett.15, 1476–1478 (1990). [CrossRef] [PubMed]
- C. Langrock, E. Diamanti, R. V. Roussev, Y. Yamamoto, M. M. Fejer, and H. Takesue, “Highly efficient single-photon detection at communication wavelengths by use of upconversion in reverse-proton-exchanged periodically poled LiNbO3 waveguides,” Opt. Lett.30, 1725–1727 (2005). [CrossRef] [PubMed]
- M. T. Rakher, L. Ma, O. Slattery, X. Tang, and K. Srinivasan, “Quantum transduction of telecommunications-band single photons from a quantum dot by frequency upconversion,” Nat. Photonics4, 786–791 (2010). [CrossRef]
- H. Takesue, “Erasing Distinguishability Using Quantum Frequency Up-Conversion,” Phys. Rev. Lett.101, 173901 (2008). [CrossRef] [PubMed]
- S. Tanzilli, W. Tittel, M. Halder, O. Alibart, P. Baldi, N. Gisin, and H. Zbinden, “A photonic quantum information interface,” Nature437, 116–120 (2005). [CrossRef] [PubMed]
- Y. Dudin, A. Radnaev, R. Zhao, J. Blumoff, T. Kennedy, and A. Kuzmich, “Entanglement of Light-Shift Compensated Atomic Spin Waves with Telecom Light,” Phys. Rev. Lett.105, 260502 (2010). [CrossRef]
- R. Ikuta, Y. Kusaka, T. Kitano, H. Kato, T. Yamamoto, M. Koashi, and N. Imoto, “Wide-band quantum interface for visible-to-telecommunication wavelength conversion,” Nat. Commun.2, 1544 (2011). [CrossRef] [PubMed]
- S. Zaske, A. Lenhard, C. Keßler, J. Kettler, C. Hepp, C. Arend, R. Albrecht, W.-M. Schulz, M. Jetter, P. Michler, and C. Becher, “Visible-to-Telecom Quantum Frequency Conversion of Light from a Single Quantum Emitter,” Phys. Rev. Lett.109, 147404 (2012). [CrossRef] [PubMed]
- R. Ikuta, H. Kato, Y. Kusaka, S. Miki, T. Yamashita, H. Terai, M. Fujiwara, T. Yamamoto, M. Koashi, M. Sasaki, Z. Wang, and N. Imoto, “High-fidelity conversion of photonic quantum information to telecommunication wavelength with superconducting single-photon detectors,” Phys. Rev. A87, 010301 (2013). [CrossRef]
- R. Ikuta, T. Kobayashi, H. Kato, S. Miki, T. Yamashita, H. Terai, M. Fujiwara, T. Yamamoto, M. Koashi, M. Sasaki, Z. Wang, and N. Imoto, “Nonclassical two-photon interference between independent telecommunication light pulses converted by difference-frequency generation,” Phys. Rev. A88, 042317 (2013). [CrossRef]
- M. Raymer, S. van Enk, C. McKinstrie, and H. McGuinness, “Interference of two photons of different color,” Opt. Commun.283, 747–752 (2010). [CrossRef]
- H. Takesue, “Single-photon frequency down-conversion experiment,” Phys. Rev. A82, 013833 (2010). [CrossRef]
- N. Curtz, R. Thew, C. Simon, N. Gisin, and H. Zbinden, “Coherent frequency-down-conversion interface for quantum repeaters,” Opt. Express18, 22099–22104 (2010). [CrossRef] [PubMed]
- S. Ramelow, a. Fedrizzi, a. Poppe, N. Langford, and a. Zeilinger, “Polarization-entanglement-conserving frequency conversion of photons,” Phys. Rev. A85, 013845 (2012). [CrossRef]
- G. Giorgi, P. Mataloni, and F. De Martini, “Frequency hopping in quantum interferometry: Efficient up-down conversion for qubits and ebits,” Phys. Rev. Lett.90, 027902 (2003). [CrossRef] [PubMed]
- S. Zaske, A. Lenhard, and C. Becher, “Efficient frequency downconversion at the single photon level from the red spectral range to the telecommunications C-band,” Opt. Express19, 12825–12836 (2011). [CrossRef] [PubMed]
- L. Ma, O. Slattery, and X. Tang, “Single photon frequency up-conversion and its applications,” Phys. Rep.521, 69–94 (2012). [CrossRef]
- T. Nishikawa, A. Ozawa, Y. Nishida, M. Asobe, F.-L. Hong, and T. W. Hänsch, “Efficient 494 mW sum-frequency generation of sodium resonance radiation at 589 nm by using a periodically poled Zn:LiNbO3 ridge waveguide,” Opt. Express17, 17792–17800 (2009). [CrossRef] [PubMed]
- S. Miki, M. Takeda, M. Fujiwara, M. Sasaki, and Z. Wang, “Compactly packaged superconducting nanowire single-photon detector with an optical cavity for multichannel system,” Opt. Express17, 23557–23564 (2009). [CrossRef]
- S. Miki, T. Yamashita, M. Fujiwara, M. Sasaki, and Z. Wang, “Multichannel SNSPD system with high detection efficiency at telecommunication wavelength,” Opt. Lett.35, 2133–2135 (2010). [CrossRef] [PubMed]
- J. S. Pelc, L. Ma, C. R. Phillips, Q. Zhang, C. Langrock, O. Slattery, X. Tang, and M. M. Fejer, “Long-wavelength-pumped upconversion single-photon detector at 1550 nm : performance and noise analysis,” Opt. Express19, 21445–21456 (2011). [CrossRef] [PubMed]

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