![]() Here, we experimentally demonstrate a nonlinear spatial quantum transport scheme for arbitrary dimensions using two entangled photons to form the quantum channel and a bright coherent source for information encoding. Although theoretical schemes have been proposed to use nonlinear approaches for high-dimensional quantum information processing and communication 31, 32, 33, none have yet been demonstrated experimentally. More recently, nonlinear optics has emerged as an exciting creation, control and detection tool for spatially structured classical light 29, but has not found its way to controlling spatially structured quantum states beyond polarisation qubit measurement 30. So far all of these approaches have used linear optics for their state control and detection, which has known limitations in the context of high-dimensional states 28. Our interest is in schemes where the information is remotely shared and not physically sent, such as teleportation, which has been limited to d = 2 using OAM 23, 24, 25 and d = 3 using the path degree of freedom 26, 27. Yet experimental progress has been slow, with sharing keys shown up to d = 6 in optical fibre 20 and d = 7 in free-space 21, and sharing secrets up to d = 11 22. In the context of spatial modes of light as a basis, orbital angular momentum (OAM) has proven particularly useful and topical 15, 16, 17, as has path 18 and pixels 19, as potential routes towards high-dimensions. ![]() Teleportation 7, 8, 9, 10 allows protected information exchange between distant parties without the need for a physical link 11, facilitated by the sharing of entangled photons and a classical communication channel, where the information sent must not be known by Alice.Īll the aforementioned schemes would benefit from using high dimensional quantum states, offering higher channel capacity 12, security 13, or resilience to noise 14. Remote state preparation 5, 6 allows information exchange between parties without transmitting the information physically across the link, but the sender (Alice) must know the information to be sent. In all these schemes, like its classical counterpart, the information is sent across a physical link between the sender and receiver. For example, quantum key distribution exchanges a key from peer to peer (usually Alice and Bob) to decode the information transmitted between communicating parties 2, quantum secret sharing splits such a key amongst many nodes 3 and quantum secure direct communication sends it without a key, but rather encoded in a transmitted quantum state 4. Quantum technologies allow this exchange to be fundamentally secure, fuelling the nascent quantum global network 1. Information exchange is the backbone of modern society, with our world connected by global networks of fibre and terrestrial links. Our demonstration merges the nascent fields of nonlinear control of structured light with quantum processes, offering a new approach to harnessing high-dimensional quantum states, and may be extended to other degrees of freedom too. We realise a d = 15 quantum channel for arbitrary photonic spatial modes which we demonstrate by faithfully transferring information encoded into orbital angular momentum, Hermite-Gaussian and arbitrary spatial mode superpositions, without requiring knowledge of the state to be sent. Using sum frequency generation we upconvert one of the photons from an entangled pair resulting in high-dimensional spatial information transported to the other. This allows us to experimentally realise quantum transport of high-dimensional spatial information facilitated by a quantum channel with a single entangled pair and a nonlinear spatial mode detector. Here we demonstrate how a nonlinear parametric process allows for arbitrary high-dimensional state projections in the spatial degree of freedom, where a strong coherent field enhances the probability of the process. Doing so with high-dimensional states offers the promise of higher information capacity and improved resilience to noise, but progress to date has been limited. ![]() Information exchange between two distant parties, where information is shared without physically transporting it, is a crucial resource in future quantum networks.
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