As the digital revolution has now become mainstream, quantum computing and quantum communication are rising in the conscious­ness of the field. The enhanced measurement technologies enabled by quantum phenomena, and the possibility of scientific progress using new methods, are of parti­cular interest to researchers around the world. Recently two researchers at Tampere University, Robert Fickler and Markus Hiekkamäki, demons­trated that two-photon inter­ference can be controlled in a near-perfect way using the spatial shape of the photon. 

“Our report shows how a complex light-shaping method can be used to make two quanta of light interfere with each other in a novel and easily tuneable way”, explains Markus Hiekka­mäki. Single photons can have highly complex shapes that could be useful for quantum techno­logies such as quantum crypto­graphy, super-sensitive measure­ments, or quantum-enhanced compu­tational tasks. To make use of these structured photons, it is crucial to make them interfere with other photons. 

“One crucial task in essen­tially all quantum technological appli­cations is improving the ability to mani­pulate quantum states in a more complex and reliable way. In photonic quantum techno­logies, this task involves changing the properties of a single photon as well as inter­fering multiple photons with each other”, says Robert Fickler, who leads the Experimental Quantum Optics group at the university. The demonstrated development is especially interesting from the point of view of high-dimen­sional quantum information science, where more than a single bit of quantum information is used per carrier. These more complex quantum states not only allow the encoding of more information onto a single photon but are also known to be more noise-resistant in various settings. 

The method presented by the research duo holds promise for building new types of linear optical networks. This paves the way for novel schemes of photonic quantum-enhanced computing. “Our experimental demons­tration of bunching two photons into multiple complex spatial shapes is a crucial next step for applying structured photons to various quantum metrological and informational tasks”, continues Markus Hiekka­mäki. 

The researchers now aim at uti­lizing the method for developing new quantum-enhanced sensing techniques, while exploring more complex spatial structures of photons and developing new approaches for compu­tational systems using quantum states. “We hope that these results inspire more research into the funda­mental limits of photon shaping. Our findings might also trigger the development of new quantum techno­logies, e.g. improved noise-tolerant quantum communi­cation or innovative quantum compu­tation schemes, that benefit from such high-dimen­sional photonic quantum states”, adds Robert Fickler. (Source: Tampere U.)

Reference: M. Hiekkamäki & R. Fickler: High-Dimensional Two-Photon Interference Effects in Spatial Modes, Phys. Rev. Lett. 126, 123601 (2021); DOI: 10.1103/PhysRevLett.126.123601

Link: Photonics Laboratory, Physics Unit, Tampere University, Tampere, Finland