Photon-Pair Generation in Periodically Poled MTiOXO4 (M=K, Rb, Cs; X=P, As)


Photon-pair production through Spontaneous parametric down-conversion, which is a nonlinear mechanism where a high energy photon decays into 2 low-energy photons, has been identified as an appropriate method for realizing heralded single-photon sources or quantum entanglement. This is particularly important for photonic quantum-information applications. Spontaneous parametric down-conversion in periodically poled nonlinear media allows for collinear propagation.

This method has been commonly referred to as quasi phase matching. Potassium titanyl phosphate, lithium tantalite, and lithium niobate are the popular nonlinear crystals that are suited for periodic poling. Several photon-pair generation applications call for a high spectral quantum purity that is comparable to frequency-uncorrelated photon pairs. Generally, Spontaneous parametric down-conversion states contain frequency entanglement, where when one of the sub-states is traced out, puts the other one into a mixed state.

In a bid to eliminate these correlations in the joint spectral distribution, a number of researchers have opted to use narrow bandpass filters, which transmit only the uncorrelated parts of the spectrum. However, bandpass filtering leads to a significant drop in count rates and heralding efficiency considering that a huge amount of the generated photons is discarded. An alternative method has been adopted where the Spontaneous parametric down-conversion process can be designed carefully such that the generated Spontaneous parametric down-conversion state is a priori frequency uncorrelated.

This approach is only practical in a closed set of cases, that is, particular crystals allow for intrinsically pure Spontaneous parametric down-conversion states only at selected wavelength and polarization configurations. Recently, a number of research works have been implemented where the joint spectral distribution is shaped by a selected custom fabrication of the poled crystals. Reference to the early development stages, this technique is restricted to the very few configurations that are known to be supported by the common nonlinear materials.

Researchers at AIT Austrian Institute of Technology GmbH and University of Vienna in collaboration with Wuhan Institute of Technology presented a comprehensive numerical investigation of five nonlinear materials as well as their features with regards to photon-pair creation via parametric down-conversion. Their research work is published in the journal, Physical Review Applied.

Periodic poling of ferromagnetic nonlinear materials has been identified as a suitable way of generating collinearly propagating photon pairs. Most researchers have adopted potassium titanyl phosphate and lithium niobate crystals for this application. In the current research, the authors provided a comprehensive discussion on the family of potassium titanyl phosphate-isomorphic nonlinear materials, which also included less common CsTiOAsO4, KTiOAsO4, RbTiOAsO4, and RbTiOPO4.

The authors observed that CsTiOAsO4 allowed for the generation of collinear photon pairs with a degenerate telecom wavelength of 1550nm, high spectral purity, and orthogonal polarization, all without ferroelectric periodic poling. The possibility of CsTiOAsO4 being used for the efficient and compact generation of polarization and frequency-entangled photon pairs with superior visibility in the telecom regime was another remarkable feature recorded by the authors.

The study by Fabian Laudenbach and colleagues will be an excellent resource for researchers who use (periodically poled and bulk) nonlinear crystals so as to generate highly performing photon pairs. It will also be helpful in the investigation and manufacture of more exotic non-linear materials.

Photon-Pair Generation in Periodically Poled MTiOXO4 (M=K, Rb, Cs; X=P, As) .. Advances in Engineering

About the author

Fabian Laudenbach is a PhD student associated to both the Faculty of Physics, University of Vienna and the Austrian Institute of Technology (AIT). He received his M.Sc. from the University of Vienna in the field of quantum optics and quantum information in 2015. Fabian joined the AIT in 2014 where he has been part of the Optical Quantum Technologies unit. His research is based on theoretical, experimental and computational quantum optics and quantum information. In particular, he has authored publications on the interface of quantum information and nonlinear optics, novel ways of entangled-photon generation, photonic integrated circuits, software-based simulations of quantum optics and communications, as well as on quantum cryptography with continuous variables and classical photonic communication technologies.

About the author

Chiara Greganti is a PhD student at the Vienna Center for Quantum Science and Technology (VCQ), Faculty of Physics, University of Vienna. She received her M.Sc. degree in Physics at the University of Rome, La Sapienza in 2012 and was a Marie-Curie Early Stage Researcher within the network Photonic Integrated Compound Quantum Encoding (PICQUE) from 2014 to 2017. Her current research focuses on telecom multi-photon experiments for quantum information processing.

About the author

Michael Hentschel graduated from the Vienna University of Technology in 1998 with a M.S. degree in Electrical Engineering and in 2001 with a PhD in the field of Femtosecond and Attosecond Lasers. After a post-doc fellowship he joined Femtolasers, Vienna in 2003 working on Femtosecond laser amplifiers. From 2006 he worked at the University of Vienna on Quantum Key Distribution with entangled photons. In 2009 he joined the Austrian Institute of Technology working on QKD systems. He has been involved in photon source development, system integration, software development, and recently in error correction on GPUs.

About the author

Philip Walther is Professor of Physics at the University of Vienna, Austria. His research is dedicated to the development of advanced photonic quantum technology for applications in quantum information processing and for investigations in quantum science. The experiments are focused on secure quantum cloud computing and quantum-secure classical computers, quantum computation and quantum simulation as well as quantum foundations such as indefinite causal structures and the measurement of weak gravitational effects on single photons using table-top setups.

He has authored numerous peer-reviewed articles, and is the recipient of the Loschmidt Prize (2005), the Fresnel Prize (2011), the Austrian START Prize (2011), the Vienna Funding Award in Science (2011), and the Recognition Award for Science by the Lower State of Austria (2014). He is Fellow of the American Physical Society (APS) and member of the Young Academy of the Austrian Academy of Sciences.

About the author

Hannes Hübel obtained his Ph.D. in physics in 2004 at Queen Mary, University of London (UK). After completing his PhD he joined the group of Prof. Zeilinger at the University of Vienna (Austria) as a postdoctoral researcher to work on entanglement based quantum key distribution. From 2007 onwards, he was group leader of the QKD group and supervised the realization and demonstration of a fully functioning autonomous entanglement-based QKD device as part of the European SECOQC project. In 2009 he moved to the Institute for Quantum Computing at the University of Waterloo (Canada) as a postdoctoral fellow and worked with Prof. Jennewein on generation of photon triplets from parametric downconversion as well as fiber and satellite based QKD. In 2011 he became an assistant professor at the physics department of the Stockholm University (Sweden), where he worked on long-distance fiber-based quantum information technologies at telecommunication wavelengths.

Since 2015 he is at the Austrian Institute of Technology in Vienna (Austria) heading the Optical Quantum Technologies unit. Dr. Hübel has authored and co-authored more than 80 publications and contributions in high impact (Nature, PRL) journals and international conferences on quantum Information. His current research activities include quantum communication with discrete and continuous variables as well as photon-pair generation in photonic integrated circuits.


Fabian Laudenbach, Rui-Bo Jin, Chiara Greganti, Michael Hentschel, Philip Walther, and Hannes Hübel. Numerical Investigation of Photon-Pair Generation in Periodically Poled MTiOXO4 (M=K, Rb, Cs; X=P, As). Physical Review Applied, volume 8,024035 (2017).


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