Biphoton shaping with cascaded entangled-photon sources

Abstract

Quantum entanglement is an integral part of quantum optics and has been exploited in areas such as computation, cryptography and metrology. The entanglement between photons can be present in various degrees of freedom (DOFs), and even the simplest bi-partite systems can occupy a large Hilbert space. Therefore, it is desirable to exploit this multi-dimensional space for various quantum applications by fully controlling the properties of the entangled photons in multiple DOFs. While current entangled-photon sources are capable of generating entanglement in one or more DOFs, there is currently a lack of practical techniques that can shape and control the entanglement properties in multiple DOFs. Here we show that cascading two or more entangled-photon sources with tunable linear media in between allows us to generate photon-pairs whose entanglement properties can be tailored and shaped in the frequency and polarisation domains. We first develop a quantum mechanical model to study the quantum state generated from the cascade structure with special considerations paid to the effects of pump temporal coherence, linear dispersion, and in-structure polarisation transformation applied between the entangled-photon sources. We then experimentally generate photon-pairs with tunable entanglement properties by manipulating the dispersion and birefringence properties of the linear medium placed in between two entangled-photon sources. This is done in an all-fibre, phase stable, and alignment-free configuration. Our results show that the cascade structure offers a great deal of flexibility in tuning the properties of entangled photons in multiple DOFs, opening up a new avenue in engineering quantum light sources.

Nonlinear interference in crystal superlattices

“…As one can see, the interference pattern contains additional contributions originating from interferometers with different gaps. The ability to manipulate the interference patterns opens up possibilities for quantum state engineering 20,35 .…”

“…Nonlinear interferometers have been realized using numerous physical platforms, including bulk nonlinear crystals [11][12][13][14][16][17][18] , gas cells 19 , fiberized networks 20,21 , and nonlinear waveguides 22,23 . Additionally, nonlinear interferometers have been used for imaging 24 , spectroscopy 16,[25][26][27] , optical coherence tomography 28,29 , superresolution interferometry 18,19 , and polarimetry 30 .…”

“…He showed that with an increase in the number of crystals, bright interference fringes in the frequency domain narrow, yet the spacing between fringes remains unchanged. This idea was theoretically expanded in more recent works 20,32,33 ; however, to the best of our knowledge, there are no reports on the experimental realization of nonlinear interferometers with more than two nonlinear elements. The major challenges in practical realization are associated with (1) the necessity of superimposing signal and idler modes from multiple nonlinear elements while preserving the quantum indistinguishability, and (2) the necessity to align and stabilize increasingly complex setups.…”

Quantum optical coherence: From linear to nonlinear interferometers

“…However, investigations into nonlinear interferometers, a subset of which are commonly labelled as SU(1,1) interferometers [18,19], have shown that these systems can be also used to characterize coherence properties of the quantum light involved and may even offer practical quantum advantages [20][21][22]. Recent experiments employing this class of interferometers have shown compelling results for both fundamental and applied physics, such as the recent demonstrations of wide-field interferometry and bi-photon shaping [23][24][25][26].…”

Recovering the full dimensionality of hyperentanglement in collinear photon pairs

“…|H /|V denotes the horizontally/vertically polarized polarized photon states and |ω s/i,n denotes the state of signal/idler photon with center frequency ω s/i,n which satisfies ω s,n +ω i,n =const [19][20][21][22]. The generation of this state has been studied in many schemes, such as a two-period quasi-phase-matching nonlinear waveguide scheme [22] and a cascaded photon pair source [23]. Notations of discretized frequency-bins are used in Eqn.(1) for the ease of discussion, but the results of this letter can also be applied to continuous frequency entanglement.…”