Quantum mechanics with patterns of light: Progress in high dimensional and multidimensional entanglement with structured light

Abstract

Quantum mechanics is now a mature topic dating back more than a century. During its scientific development, it fostered many technological advances that now are integrated into our everyday lives. More recently, over the past few decades, the authors have seen the emergence of a second quantum revolution, ushering in control of quantum states. Here, the spatial modes of light, “patterns of light,” hold tremendous potential: light is weakly interacting and so an attractive avenue for exploring entanglement preservation in open systems, while spatial modes of light offer a route to high dimensional Hilbert spaces for larger encoding alphabets, promising higher information capacity per photon, better security, and enhanced robustness to noise. Yet, progress in harnessing high dimensional spatial mode entanglement remains in its infancy. Here, the authors review the recent progress in this regard, outlining the core concepts in a tutorial manner before delving into the advances made in creation, manipulation, and detection of such quantum states. The authors cover advances in using orbital angular momentum as well as vectorial states that are hybrid entangled, combining spatial modes with polarization to form an infinite set of two-dimensional spaces: multidimensional entanglement. The authors highlight the exciting work in pushing the boundaries in both the dimension and the photon number, before finally summarizing the open challenges, and the questions that remain unanswered.

Structured Light in Turbulence

“…Quantum communication with high dimensional spatial modes of light has received much interest in the quantum optics community with hopes of playing a substantial role in the future of global quantum networks to be deployed in our all-pervading noisy atmosphere [28], [35], [190][191][192].…”

“…The idea has been around since the 1980s in fibre and gained momentum in the past 10 years after seminal MDM demonstrations [10][11][12], inspired by work of the Nakazawa group. In free-space the development followed advances in orbital angular momentum (OAM), one of which was a proof-of-principle demonstration of communication down a corridor in the University of Glasgow [13], with many seminal demonstrations quickly following [14][15][16] including interesting applications such as communications to aerial platforms [17], and later with other mode sets [18][19][20][21][22][23][24], as well as with quantum states in the spatial mode basis [25][26][27][28][29][30][31][32][33][34].…”

Experimental Demonstration of 11‐Dimensional 10‐Party Quantum Secret Sharing

“…Alternatively, the orbital angular momentum (OAM) [ 16,17 ] degree of freedom of light offers access to an infinite‐dimensional Hilbert space and is thus a promising candidate for scalable high‐dimensional quantum information processes. [ 18 ] Indeed, the OAM of light (scalar and vector) has been used to demonstrate the feasibility of high‐dimensional quantum cryptography over free‐space, [ 19–22 ] optical fiber [ 23,24 ] and underwater. [ 25 ] In the context of QSS, high‐dimensional single photon secret sharing has only been demonstrated with at most three dimensions using spatial modes of light.…”

Quantum key distribution over free space optic (FSO) channel using higherorder Gaussian beam spatial modes

“…If the incoming photon state is conjugate with respect to the phase hologram of SLM, then the nonzero value of ℓ will be converted into standard Gaussian T EM 00 like mode and impacts on the SM fiber along the axis of the fiber and hence increments the photon count. Alternatively, other modes will be nullified and no photons detected or sorted [40,49]. The SM fiber paths are then merged optically and then both of the outputs are directed towards single-photon counting block or single photon avalanche diode (SPAD) as shown in Figure 3.…”