Summary form only given. This paper investigates different approaches to generate optical quantum states by means of integrated optical frequency combs. These include the generation of multiplexed heralded single-photons, the first realization of cross-polarized photon-pairs on a photonic chip, the first generation of multiple two-photon entangled states, and the first realizations of multi-photon entangled quantum states on a photonic chip

Bromberg, Yaron

Caspani, Lucia

Chu, Sai T.

Kues, Michael

Little, Brent E.

Morandotti, Roberto

Moss, David J.

Reimer, Christian

Roztocki, Piotr

Sciara, Stefania

Wetzel, Benjamin

English

Stefania Sciara

Michael Kues

Christian Reimer

Piotr Roztocki

Benjamin Wetzel

Yaron Bromberg

Brent E. Little

Sai T. Chu

David J. Moss

Lucia Caspani

Roberto Morandotti

Crossref

On-chip quantum state generation by means of integrated frequency combs

Enlighten

    Sciara, S. et al. (2017) On-chip Quantum State Generation by Means of Integrated Frequency Combs. In: IEEE Photonics Society Summer Topical Meeting Series (SUM 2017), San Juan, Puerto Rico, 10-12 Jul 2017, pp. 181-182. ISBN 9781509065714 (doi:10.1109/PHOSST.2017.8012710)  This is the author’s final accepted version.  There may be differences between this version and the published version. You are advised to consult the publisher’s version if you wish to cite from it.     http://eprints.gla.ac.uk/149998/            Deposited on: 18 October 2017              Enlighten – Research publications by members of the University of Glasgow http://eprints.gla.ac.uk   1   On-chip Quantum State Generation by means of Integrated Frequency Combs  Stefania Sciara1,2, Michael Kues1,3,*, Christian Reimer1, Piotr Roztocki1, Benjamin Wetzel1,4, Yaron Bromberg5, Brent E. Little6, Sai T. Chu7, David J. Moss8, Lucia Caspani9, and Roberto Morandotti1,**  1 INRS-EMT, 1650 Boulevard Lionel Boulet, Varennes, Québec J3X 1S2, Canada  2 University of Palermo-Department of Energy, Information Engineering and Mathematical Methods, Palermo 90128, Italy 3School of Engineering, University of Glasgow, Rankine Building, Oakfield Avenue, Glasgow G12 8LT, Scotland 4Department of Physics and Astronomy, University of Sussex, Falmer, Brighton BN1 9RH, England 5 Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem 91904, Israel 6 Xi’an Institute of Optics and Precision Mechanics of CAS, Xi’an, China 7Department of Physics and Material Science, City University of Hong Kong, Tat Chee Avenue, Hong Kong, China 8Centre for Micro Photonics, Swinburne University of Technology, Hawthorn, VIC, 3122 Australia 9Institute of Photonics, Department of Physics, University of Strathclyde, Glasgow G4 0NW, Scotland  * michael.kues@emt.inrs.ca, **morandotti@emt.inrs.ca   Entangled photon-pair sources are key building blocks towards the realization of applications in quantum information processing [1], quantum communications [2], as well as imaging and sensing with resolutions exceeding the classical limit [3]. The generation of, e.g. polarization, time-energy and time-bin entangled photon-pairs has been demonstrated using spontaneous parametric down-conversion (SPDC) in nonlinear second-order media, as well as spontaneous four-wave mixing (SFWM) in third-order nonlinear media. Specifically, nonlinear (third-order) interactions in on-chip microring resonators have been widely used to achieve classical frequency combs [4], mode-lock lasers [5], signal processing [6], etc. Integrated photonics can also find applications for quantum state generation in compact, scalable and efficient devices, required for future optical quantum circuits. In particular, solutions focusing on an integrated (on-chip) approach have been recently investigated and developed, including integrated quantum circuits, sources and detectors [7]. In contrast to waveguides, microring resonators [8] with narrow resonances and high Q-factors, offer an improvement in photon-pair generation efficiency, as well as a narrow photon-pair bandwidth, making them compatible with quantum optical devices (e.g. high temporal-resolution single-photon detectors and quantum memories). Most importantly, in contrast to non-resonant waveguides, where individuals photon-pairs, featured by one signal/idler frequency pair, are generally produced, resonant nonlinear cavities (e.g., microring resonators) allow the generation of correlated photon-pairs on multiple signal/idler frequency channels [9], due to their periodic and equidistant resonance structure.  Here, we investigate different approaches to generate optical quantum states by means of integrated optical frequency combs. These include the generation of multiplexed heralded single-photons [9], the first realization of cross-polarized photon-pairs on a photonic chip [10], the first generation of multiple two-photon entangled states [11], and the first realizations of multi-photon entangled quantum states on a photonic chip [11]. The quantum frequency combs were realized by using a 4-port integrated microring resonator with a free spectral range (FSR) of 200 GHz, fabricated in a CMOS-compatible high refractive index silica glass [12]. The resonators were excited with a pulsed mode-locked fiber laser. The high resonator field enhancement and the high nonlinearity allowed generating photon-pairs through SFWM on several frequency channels (corresponding to the ring resonances) symmetrically located with respect to the pump frequency [9]. Depending on the targeted application, different excitation schemes were used. If the pump spectral bandwidth was chosen to be larger than the resonator bandwidth, the laser was spectrally-filtered to excite a single or multiple resonances. The coupling into the resonator then further spectrally filtered the pump to perfectly match the bandwidth of the resonator. This configuration enabled the generation of pure single frequency-mode photons [11]. Coincidence detection was used to characterize the photon coincidence statistics and their temporal duration. We measured the (heralded) second-order coherence of the emitted photons using a Hanbury Brown and Twiss setup. In order to create time-bin entangled photons, an unbalanced phase-stabilized Michelson interferometer generating double pulses was used before the chip. If the pump power was then set to generate no more than one photon-pair per double pulse on average,   2  the photon-pairs were created in a coherent superposition of two discrete time-bins, thus forming an entangled state [11]. To verify entanglement through quantum interference, we added interferometers with the path length difference matched to the first interferometer. Using coincidence detection, this setup allowed to measure quantum interference and perform full quantum state tomography, which characterize the entangled photon-pairs and multi-photon states. By simultaneously exciting two orthogonal-polarization mode resonances, we introduced a new type of SFWM to the toolbox of integrated photonics [10]. In particular, we demonstrated the first realization of type-II SFWM that allows to directly generate orthogonally-polarized photon-pairs on a chip [10]. We measured photon coincidences, and also drive the system to optical parametric oscillation, generating orthogonally-polarized beams. Using double pulse excitation, we demonstrated time-bin entangled photon-pairs over the entire frequency comb spectrum [11]. We measured the violation of a Bell-like inequality through quantum interference [13] both on co-, as well as cross-polarized photon-pairs. Performing quantum state tomography [14], we confirmed qubit entanglement with fidelities above 85%, enabling the implementation of quantum information processing protocols [15]. We repeated tomography measurements after 40 km of fiber propagation, and confirmed that the quantum states are well preserved during propagation. This opens up possible implementations in quantum communications applications. Finally, we achieved the generation of multiple photon-pairs on different frequency mode pairs simultaneously. By measuring four-photon coincidences, quantum interference and tomography, we confirmed the generation of four-photon time-bin entangled product states, which represent the first realization of multi-photon entanglement on a photonic chip [11]. In conclusion, we demonstrate the realization of different optical quantum states by means of integrated optical frequency comb sources. Our results indicate the strong potential to use on-chip frequency combs to generate both heralded single photons and two/multi-photon entangled states.  References  1. P. Walther et al., “Experimental one-way quantum computing”, Nature 434, 169 (2005) 2. H. J. Kimble, “The quantum internet”, Nature 453, 1023 (2008)  3. M. Kolobov, “The spatial behavior of nonclassical light”, Rev. Mod. Phys. 71, 1539 (1999)  4. T. J. Kippenberg et al., “Microresonator-based optical frequency combs”, Science 332, 555 (2011) 5. M. Kues et al., “Passively mode-locked laser with an ultra-narrow spectral width”, Nature Photon. 11, 159-162 (2017)  6. M. Ferrera et al., “On-chip CMOS –compatible all-optical integrator”, Nature Commun. 1, 29 (2010)  7. D. Bonneau et al., “Silicon quantum photonics”, in Silicon Photonics III, L. Pavesi, D.J. Lockwood, Springer, pp. 41-82 8. D. Grassani et al., “Micrometer-scale integrated silicon source of time-energy entangled photons”, Optica 2, 88 (2015) 9. C. Reimer et al., “Integrated frequency comb source of heralded single photons”, Opt. Express 22, 1023 (2014) 10. C. Reimer et al., “Cross-polarized photon-pair generation and bi-chromatically pumped optical parametric oscillation on a chip”, Nature Commun. 6, 8236 (2015) 11. C. Reimer et al., “Generation of multiphoton entangled quantum states by means of integrated frequency combs”, Science 351, 1176 (2016) 12. D. J. Moss et al., “New CMOS-compatible platforms based on silicon nitride and Hydex for nonlinear optics”, Nature Photon. 7, 597 (2013) 13. J. F. Clauser et al., “Proposed experiment to test local hidden-variable theories”, Phys. Rev. Lett. 23, 880 (1969) 14. D. F. V. James et al., “Measurement of qubits”, Phys. Rev. A. 64, 052312 (2001) 15. P. C. Humphreys et al., “Linear optical quantum computing in a single spatial mode”, Phys. Rev. Lett. 111, 150501 (2013) 

On-chip Quantum State Generation by Means of Integrated Frequency Combs

Enlighten: Publications

 
 
 
 
Sciara, S. et al. (2017) On-chip Quantum State Generation by Means of 
Integrated Frequency Combs. In: IEEE Photonics Society Summer Topical 
Meeting Series (SUM 2017), San Juan, Puerto Rico, 10-12 Jul 2017, pp. 
181-182. ISBN 9781509065714 (doi:10.1109/PHOSST.2017.8012710) 
 
This is the author’s final accepted version. 
 
There may be differences between this version and the published version. 
You are advised to consult the publisher’s version if you wish to cite from 
it. 
 
 
 
 
http://eprints.gla.ac.uk/149998/ 
     
 
 
 
 
 
 
Deposited on: 18 October 2017 
 
 
 
 
 
 
 
 
 
 
 
 
 
Enlighten – Research publications by members of the University of Glasgow 
http://eprints.gla.ac.uk 
  
1 
 
 
On-chip Quantum State Generation by means of Integrated Frequency Combs 
 
Stefania Sciara1,2, Michael Kues1,3,*, Christian Reimer1, Piotr Roztocki1, Benjamin Wetzel1,4, Yaron Bromberg5, Brent E. Little6, 
Sai T. Chu7, David J. Moss8, Lucia Caspani9, and Roberto Morandotti1,** 
 
1 INRS-EMT, 1650 Boulevard Lionel Boulet, Varennes, Québec J3X 1S2, Canada  
2 University of Palermo-Department of Energy, Information Engineering and Mathematical Methods, Palermo 90128, Italy 
3School of Engineering, University of Glasgow, Rankine Building, Oakfield Avenue, Glasgow G12 8LT, Scotland 
4Department of Physics and Astronomy, University of Sussex, Falmer, Brighton BN1 9RH, England 
5 Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem 91904, Israel 
6 Xi’an Institute of Optics and Precision Mechanics of CAS, Xi’an, China 
7Department of Physics and Material Science, City University of Hong Kong, Tat Chee Avenue, Hong Kong, China 
8Centre for Micro Photonics, Swinburne University of Technology, Hawthorn, VIC, 3122 Australia 
9Institute of Photonics, Department of Physics, University of Strathclyde, Glasgow G4 0NW, Scotland  
* michael.kues@emt.inrs.ca, **morandotti@emt.inrs.ca  
 
Entangled photon-pair sources are key building blocks towards the realization of applications in 
quantum information processing [1], quantum communications [2], as well as imaging and sensing with 
resolutions exceeding the classical limit [3]. The generation of, e.g. polarization, time-energy and time-bin 
entangled photon-pairs has been demonstrated using spontaneous parametric down-conversion (SPDC) in 
nonlinear second-order media, as well as spontaneous four-wave mixing (SFWM) in third-order nonlinear 
media. Specifically, nonlinear (third-order) interactions in on-chip microring resonators have been widely 
used to achieve classical frequency combs [4], mode-lock lasers [5], signal processing [6], etc. Integrated 
photonics can also find applications for quantum state generation in compact, scalable and efficient devices, 
required for future optical quantum circuits. In particular, solutions focusing on an integrated (on-chip) 
approach have been recently investigated and developed, including integrated quantum circuits, sources 
and detectors [7]. In contrast to waveguides, microring resonators [8] with narrow resonances and high Q-
factors, offer an improvement in photon-pair generation efficiency, as well as a narrow photon-pair 
bandwidth, making them compatible with quantum optical devices (e.g. high temporal-resolution single-
photon detectors and quantum memories). Most importantly, in contrast to non-resonant waveguides, where 
individuals photon-pairs, featured by one signal/idler frequency pair, are generally produced, resonant 
nonlinear cavities (e.g., microring resonators) allow the generation of correlated photon-pairs on multiple 
signal/idler frequency channels [9], due to their periodic and equidistant resonance structure.  
Here, we investigate different approaches to generate optical quantum states by means of integrated 
optical frequency combs. These include the generation of multiplexed heralded single-photons [9], the first 
realization of cross-polarized photon-pairs on a photonic chip [10], the first generation of multiple two-
photon entangled states [11], and the first realizations of multi-photon entangled quantum states on a 
photonic chip [11]. 
The quantum frequency combs were realized by using a 4-port integrated microring resonator with 
a free spectral range (FSR) of 200 GHz, fabricated in a CMOS-compatible high refractive index silica glass 
[12]. The resonators were excited with a pulsed mode-locked fiber laser. The high resonator field 
enhancement and the high nonlinearity allowed generating photon-pairs through SFWM on several 
frequency channels (corresponding to the ring resonances) symmetrically located with respect to the pump 
frequency [9]. Depending on the targeted application, different excitation schemes were used. If the pump 
spectral bandwidth was chosen to be larger than the resonator bandwidth, the laser was spectrally-filtered 
to excite a single or multiple resonances. The coupling into the resonator then further spectrally filtered the 
pump to perfectly match the bandwidth of the resonator. This configuration enabled the generation of pure 
single frequency-mode photons [11]. Coincidence detection was used to characterize the photon 
coincidence statistics and their temporal duration. We measured the (heralded) second-order coherence of 
the emitted photons using a Hanbury Brown and Twiss setup. In order to create time-bin entangled photons, 
an unbalanced phase-stabilized Michelson interferometer generating double pulses was used before the 
chip. If the pump power was then set to generate no more than one photon-pair per double pulse on average, 
  
2 
 
the photon-pairs were created in a coherent superposition of two discrete time-bins, thus forming an 
entangled state [11]. To verify entanglement through quantum interference, we added interferometers with 
the path length difference matched to the first interferometer. Using coincidence detection, this setup 
allowed to measure quantum interference and perform full quantum state tomography, which characterize 
the entangled photon-pairs and multi-photon states. 
By simultaneously exciting two orthogonal-polarization mode resonances, we introduced a new 
type of SFWM to the toolbox of integrated photonics [10]. In particular, we demonstrated the first 
realization of type-II SFWM that allows to directly generate orthogonally-polarized photon-pairs on a chip 
[10]. We measured photon coincidences, and also drive the system to optical parametric oscillation, 
generating orthogonally-polarized beams. 
Using double pulse excitation, we demonstrated time-bin entangled photon-pairs over the entire 
frequency comb spectrum [11]. We measured the violation of a Bell-like inequality through quantum 
interference [13] both on co-, as well as cross-polarized photon-pairs. Performing quantum state 
tomography [14], we confirmed qubit entanglement with fidelities above 85%, enabling the implementation 
of quantum information processing protocols [15]. We repeated tomography measurements after 40 km of 
fiber propagation, and confirmed that the quantum states are well preserved during propagation. This opens 
up possible implementations in quantum communications applications. 
Finally, we achieved the generation of multiple photon-pairs on different frequency mode pairs 
simultaneously. By measuring four-photon coincidences, quantum interference and tomography, we 
confirmed the generation of four-photon time-bin entangled product states, which represent the first 
realization of multi-photon entanglement on a photonic chip [11]. 
In conclusion, we demonstrate the realization of different optical quantum states by means of 
integrated optical frequency comb sources. Our results indicate the strong potential to use on-chip frequency 
combs to generate both heralded single photons and two/multi-photon entangled states. 
 
References  
1. P. Walther et al., “Experimental one-way quantum computing”, Nature 434, 169 (2005) 
2. H. J. Kimble, “The quantum internet”, Nature 453, 1023 (2008)  
3. M. Kolobov, “The spatial behavior of nonclassical light”, Rev. Mod. Phys. 71, 1539 (1999)  
4. T. J. Kippenberg et al., “Microresonator-based optical frequency combs”, Science 332, 555 (2011) 
5. M. Kues et al., “Passively mode-locked laser with an ultra-narrow spectral width”, Nature Photon. 11, 
159-162 (2017)  
6. M. Ferrera et al., “On-chip CMOS –compatible all-optical integrator”, Nature Commun. 1, 29 (2010)  
7. D. Bonneau et al., “Silicon quantum photonics”, in Silicon Photonics III, L. Pavesi, D.J. Lockwood, 
Springer, pp. 41-82 
8. D. Grassani et al., “Micrometer-scale integrated silicon source of time-energy entangled photons”, 
Optica 2, 88 (2015) 
9. C. Reimer et al., “Integrated frequency comb source of heralded single photons”, Opt. Express 22, 1023 
(2014) 
10. C. Reimer et al., “Cross-polarized photon-pair generation and bi-chromatically pumped optical 
parametric oscillation on a chip”, Nature Commun. 6, 8236 (2015) 
11. C. Reimer et al., “Generation of multiphoton entangled quantum states by means of integrated 
frequency combs”, Science 351, 1176 (2016) 
12. D. J. Moss et al., “New CMOS-compatible platforms based on silicon nitride and Hydex for nonlinear 
optics”, Nature Photon. 7, 597 (2013) 
13. J. F. Clauser et al., “Proposed experiment to test local hidden-variable theories”, Phys. Rev. Lett. 23, 
880 (1969) 
14. D. F. V. James et al., “Measurement of qubits”, Phys. Rev. A. 64, 052312 (2001) 
15. P. C. Humphreys et al., “Linear optical quantum computing in a single spatial mode”, Phys. Rev. Lett. 
111, 150501 (2013) 



	Entangled photon-pair sources are key building blocks towards the realization of applications in quantum information processing [1], quantum communications [2], as well as imaging and sensing with resolutions exceeding the classical limit [3]. The generation of, e.g. polarization, time-energy and time-bin entangled photon-pairs has been demonstrated using spontaneous parametric down-conversion (SPDC) in nonlinear second-order media, as well as spontaneous four-wave mixing (SFWM) in third-order nonlinear media. Specifically, nonlinear (third-order) interactions in on-chip microring resonators have been widely used to achieve classical frequency combs [4], mode-lock lasers [5], signal processing [6], etc. Integrated photonics can also find applications for quantum state generation in compact, scalable and efficient devices, required for future optical quantum circuits. In particular, solutions focusing on an integrated (on-chip) approach have been recently investigated and developed, including integrated quantum circuits, sources and detectors [7]. In contrast to waveguides, microring resonators [8] with narrow resonances and high Q-factors, offer an improvement in photon-pair generation efficiency, as well as a narrow photon-pair bandwidth, making them compatible with quantum optical devices (e.g. high temporal-resolution single-photon detectors and quantum memories). Most importantly, in contrast to non-resonant waveguides, where individuals photon-pairs, featured by one signal/idler frequency pair, are generally produced, resonant nonlinear cavities (e.g., microring resonators) allow the generation of correlated photon-pairs on multiple signal/idler frequency channels [9], due to their periodic and equidistant resonance structure. &copy; 2017 IEEE.</p

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On-chip Quantum State Generation by Means of Integrated Frequency Combs

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