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The Hong-Ou-Mandel interferometer; critical design aspects and a new procedure for alignment.

Peter James Thomas, Jessica Y. Cheung, Christopher J. Chunnilall, Malcolm H. Dunn

Published Jan 1, 2009• 0 citations
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Abstract

The critical design aspects of a free space Hong-Ou-Mandel interferometer illuminated with pair photons from a non-collinearly phasematched spontaneous parametric downconversion process are discussed. In particular the efficient generation and collection of pair photons at a specified wavelength and a procedure for constructing the interferometer are presented. Two major requirements in the construction are the alignment and length-balancing of two optical paths, which were achieved using a new method incorporating long and short coherence length light sources, and requiring no custom optics or expensive equipment. The method balanced the optical paths to within an average of 11.6 mm, considerably shortening set-up time and two-photon interference features with visibilities ~ 0.9 were produced. The importance of interferometer characterization is discussed in the context of the application of Hong-Ou-Mandel interferometry to single photon source evaluation.

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The Hong–Ou–Mandel interferometer: A new procedure for alignment

Peter James Thomas, Jessica Y. Cheung, Christopher J. Chunnilall +1 more

Two major requirements in the construction of the Hong-Ou-Mandel interferometer are the alignment and length balancing of two optical paths. A new method is presented for meeting these requirements that requires no custom optics or expensive equipment. Using this method, a two photon interferometer sourced by degenerate noncollinear parametric photon pairs was aligned and the optical paths were balanced to within an average of 11.6 microm, yielding two-photon interference features with visibilities of approximately 0.9. The method is applicable to arbitrary noncollinear emission angles, including nondegenerate downconversion situations where the signal and idler emission angles differ.

Review of Scientific Instruments•Mar 1, 2009•6 citations

Phase-tunable inverse Hong-Ou-Mandel interference: Principles and demonstration in a photon pair source

Csaba Tamás Holló, Tamás Sarkadi, Attila Barócsi +2 more

A method is presented for the separation of polarization-entangled, frequency-degenerate photon pairs based on inverse Hong-Ou-Mandel interference. Adjusting the phase between photon states is achieved by exploiting the wavelength dispersion of optical glass, for which process a complete mathematical description is given. To experimentally demonstrate the phenomenon, a custom photon pair source has been built using spontaneous parametric downconversion of type-0 phase matching and a Sagnac interferometer. The effect of phase tuning was characterized by the modulation of coincidence probability. The visibility of quantum interference was found to be 0.820 and 0.720 for photons being in purely horizontal or vertical polarization state. In case of polarization entanglement, the measured state fidelity with respect to the $|{\mathrm{\ensuremath{\Phi}}}^{\ensuremath{-}}\ensuremath{\rangle}$ Bell state was 0.914.

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We present and demonstrate a method for balancing the two paths of a two-photon interferometer of the Hong-Ou-Mandel (HOM) variety. This method removes the difficulties of balancing the paths in this type of interferometer where a type-I crystal is used for the generation of the entangled photon pairs. Using this method we show that we are consistently able to balance the ∼2000 mm path lengths in our HOM interferometer on average to within ∼60 μm.

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The application of spontaneous parametric downconversion to develop tools for validating photonic quantum information technologies

Peter James Thomas

This portfolio of work contributes to the remit of the National Physical Laboratory (NPL) to develop the underpinning expertise and tools for validating nascent and future optical quantum technologies based on the discrete and quantum properties of photons. This requirement overlaps with the requirement to provide validation for devices operating in the photon-counting regime. A common theme running through the portfolio is photon pairs generated through spontaneous parametric downconversion (SPDC). \n \nA Hong-Ou-Mandel (HOM) interferometer sourced with visible wavelength photon pairs from an SPDC process in beta-barium borate (BBO) was designed, built and characterised. The visibility of the HOM interference is dependent on the indistinguishability of the interfering photons, but is also influenced by imperfections of the interferometer; therefore an investigation was carried out to quantify the effects of the interferometer imperfections on the measured visibility so that the true photon indistinguishability could be measured with a quantified uncertainty. \n \nA bright source of correlated pair photons in the telecoms band based upon a pump enhanced SPDC process in periodically-poled potassium titanyl phosphate (PPKTP) was designed, built and characterised. From the characterisation measurements the source brightness was estimated to be 6.2×10⁴ pairs/ s/ mw pump. The photon pairs were further characterised through their incorporation as a source in a HOM interference experiment. \n \nThe developed correlated photon pair source was at the heart of a novel scheme for the generation of polarisation entangled photon pairs, for which the design, build and characterisation work is presented. The source was demonstrated to produce two of the four maximally entangled Bell states with quantum interference visibilities of around 0.95. The generated states were also shown to break a form of Bell’s inequality by around six standard deviations. The polarisation entangled photon pair source was originally built at the University of St Andrews and was later transferred to the NPL where it will extend NPL’s capabilities to this key spectral region. \n \nFinally a study was carried out to investigate the possibility of a wavelength tuneable device for the absolute measurement of single photon detector quantum efficiencies based upon an established SPDC technique.

•Nov 30, 2010•0 citations

Generalized quantum interference of correlated photon pairs

Heonoh Kim, Sang Min Lee, Han Seb Moon

Superposition and indistinguishablility between probability amplitudes have played an essential role in observing quantum interference effects of correlated photons. The Hong-Ou-Mandel interference and interferences of the path-entangled photon number state are of special interest in the field of quantum information technologies. However, a fully generalized two-photon quantum interferometric scheme accounting for the Hong-Ou-Mandel scheme and path-entangled photon number states has not yet been proposed. Here we report the experimental demonstrations of the generalized two-photon interferometry with both the interferometric properties of the Hong-Ou-Mandel effect and the fully unfolded version of the path-entangled photon number state using photon-pair sources, which are independently generated by spontaneous parametric down-conversion. Our experimental scheme explains two-photon interference fringes revealing single- and two-photon coherence properties in a single interferometer setup. Using the proposed interferometric measurement, it is possible to directly estimate the joint spectral intensity of a photon pair source.

arXiv:1503.08611•Scientific Reports•May 7, 2015•21 citations

Matching two long interferometric pathlengths using low temporal coherence light for finding Hong–Ou–Mandel dip

Keith A. Wyman, Noah S. Everett, Anil K. Patnaik

Abstract Hong–Ou–Mandel (HOM) dip from a biphoton source in a two-photon interferometer provides a myriad of quantum tools for quantum communication and sensing. But the stringent requirements for spatial coherence between the photon pair makes it prohibitively difficult to observe high-fidelity HOM dip in long-distance free-space implementations, e.g., for the photon pairs involved in quantum communication need to match the two path lengths within a few 10 s of micron because of the short coherence width of the two-photon wave-packet. While many techniques for the pathlength balancing of two interferometric arms have been studied and applied extensively, such balancing is further complicated in presence of turbulence in long-distance free-space propagation. On a table-top testbed with each arm of a Mach–Zehnder interferometer (MZI) $$\sim 10$$ ∼ 10 -meter long in our turbulent atmospheric simulator for qubit (TASQ), we have employed below-threshold lasers to achieve classical low-coherence interferometry and show that we could narrow down the interrogation window for the pathlength balancing to obtain interference peak at the center. This method allowed us to reduce the interrogation distance for searching the HOM dip by four orders of magnitude, i.e., from tens of centimeters to a few tens of micron. Such pathlength balancing allowed realizing the HOM dip within $$160\,\upmu \textrm{m}$$ 160 μ m distance from the peak of the classical interference fringe. This technique could be helpful in a wide variety of long-pathlength interference-based quantum sensing.

The European Physical Journal Special Topics•Jun 5, 2026•1 citation
The critical design aspects of a free space Hong-Ou-Mandel interferometer illuminated with pair photons from a non-collinearly phasematched spontaneous parametric downconversion process are discussed. In particular the efficient generation and collection of pair photons at a specified wavelength and a procedure for constructing the interferometer are presented. Two major requirements in the construction are the alignment and length-balancing of two optical paths, which were achieved using a new method incorporating long and short coherence length light sources, and requiring no custom optics or expensive equipment. The method balanced the optical paths to within an average of 11.6 mm, considerably shortening set-up time and two-photon interference features with visibilities ~ 0.9 were produced. The importance of interferometer characterization is discussed in the context of the application of Hong-Ou-Mandel interferometry to single photon source evaluation.
Two major requirements in the construction of the Hong-Ou-Mandel interferometer are the alignment and length balancing of two optical paths. A new method is presented for meeting these requirements that requires no custom optics or expensive equipment. Using this method, a two photon interferometer sourced by degenerate noncollinear parametric photon pairs was aligned and the optical paths were balanced to within an average of 11.6 microm, yielding two-photon interference features with visibilities of approximately 0.9. The method is applicable to arbitrary noncollinear emission angles, including nondegenerate downconversion situations where the signal and idler emission angles differ.
A method is presented for the separation of polarization-entangled, frequency-degenerate photon pairs based on inverse Hong-Ou-Mandel interference. Adjusting the phase between photon states is achieved by exploiting the wavelength dispersion of optical glass, for which process a complete mathematical description is given. To experimentally demonstrate the phenomenon, a custom photon pair source has been built using spontaneous parametric downconversion of type-0 phase matching and a Sagnac interferometer. The effect of phase tuning was characterized by the modulation of coincidence probability. The visibility of quantum interference was found to be 0.820 and 0.720 for photons being in purely horizontal or vertical polarization state. In case of polarization entanglement, the measured state fidelity with respect to the $|{\mathrm{\ensuremath{\Phi}}}^{\ensuremath{-}}\ensuremath{\rangle}$ Bell state was 0.914.
This portfolio of work contributes to the remit of the National Physical Laboratory (NPL) to develop the underpinning expertise and tools for validating nascent and future optical quantum technologies based on the discrete and quantum properties of photons. This requirement overlaps with the requirement to provide validation for devices operating in the photon-counting regime. A common theme running through the portfolio is photon pairs generated through spontaneous parametric downconversion (SPDC). \n \nA Hong-Ou-Mandel (HOM) interferometer sourced with visible wavelength photon pairs from an SPDC process in beta-barium borate (BBO) was designed, built and characterised. The visibility of the HOM interference is dependent on the indistinguishability of the interfering photons, but is also influenced by imperfections of the interferometer; therefore an investigation was carried out to quantify the effects of the interferometer imperfections on the measured visibility so that the true photon indistinguishability could be measured with a quantified uncertainty. \n \nA bright source of correlated pair photons in the telecoms band based upon a pump enhanced SPDC process in periodically-poled potassium titanyl phosphate (PPKTP) was designed, built and characterised. From the characterisation measurements the source brightness was estimated to be 6.2×10⁴ pairs/ s/ mw pump. The photon pairs were further characterised through their incorporation as a source in a HOM interference experiment. \n \nThe developed correlated photon pair source was at the heart of a novel scheme for the generation of polarisation entangled photon pairs, for which the design, build and characterisation work is presented. The source was demonstrated to produce two of the four maximally entangled Bell states with quantum interference visibilities of around 0.95. The generated states were also shown to break a form of Bell’s inequality by around six standard deviations. The polarisation entangled photon pair source was originally built at the University of St Andrews and was later transferred to the NPL where it will extend NPL’s capabilities to this key spectral region. \n \nFinally a study was carried out to investigate the possibility of a wavelength tuneable device for the absolute measurement of single photon detector quantum efficiencies based upon an established SPDC technique.
Superposition and indistinguishablility between probability amplitudes have played an essential role in observing quantum interference effects of correlated photons. The Hong-Ou-Mandel interference and interferences of the path-entangled photon number state are of special interest in the field of quantum information technologies. However, a fully generalized two-photon quantum interferometric scheme accounting for the Hong-Ou-Mandel scheme and path-entangled photon number states has not yet been proposed. Here we report the experimental demonstrations of the generalized two-photon interferometry with both the interferometric properties of the Hong-Ou-Mandel effect and the fully unfolded version of the path-entangled photon number state using photon-pair sources, which are independently generated by spontaneous parametric down-conversion. Our experimental scheme explains two-photon interference fringes revealing single- and two-photon coherence properties in a single interferometer setup. Using the proposed interferometric measurement, it is possible to directly estimate the joint spectral intensity of a photon pair source.
Abstract Hong–Ou–Mandel (HOM) dip from a biphoton source in a two-photon interferometer provides a myriad of quantum tools for quantum communication and sensing. But the stringent requirements for spatial coherence between the photon pair makes it prohibitively difficult to observe high-fidelity HOM dip in long-distance free-space implementations, e.g., for the photon pairs involved in quantum communication need to match the two path lengths within a few 10 s of micron because of the short coherence width of the two-photon wave-packet. While many techniques for the pathlength balancing of two interferometric arms have been studied and applied extensively, such balancing is further complicated in presence of turbulence in long-distance free-space propagation. On a table-top testbed with each arm of a Mach–Zehnder interferometer (MZI) ∼10\sim 10∼10 ∼ 10 -meter long in our turbulent atmospheric simulator for qubit (TASQ), we have employed below-threshold lasers to achieve classical low-coherence interferometry and show that we could narrow down the interrogation window for the pathlength balancing to obtain interference peak at the center. This method allowed us to reduce the interrogation distance for searching the HOM dip by four orders of magnitude, i.e., from tens of centimeters to a few tens of micron. Such pathlength balancing allowed realizing the HOM dip within $$160\,\upmu \textrm{m}$$ 160 μ m distance from the peak of the classical interference fringe. This technique could be helpful in a wide variety of long-pathlength interference-based quantum sensing.