Real-time imaging of photonic quantum teleportation

Abstract

The science fiction depiction of teleportation refers to the transfer of matter between two spatially separated spaces without the transfer of information. This largely differs from the concept of quantum teleportation, one of the most exciting concepts in modern quantum theory, though often misunderstood.1 The key difference between the sci-fi portrayal and quantum teleportation is that information is transferred between two spatially separated parties, rather than a direct transfer of matter. Applications may include quantum key distribution and quantum cryptography. At the heart of such teleportation is the phenomenon of quantum entanglement, in which the quantum state corresponding to non-local particles cannot be described independently. Sender (Alice) and receiver (Bob) share a pair of particles that are entangled. Alice performs a set of measurements (known as the Bell states analysis) on the state of her particle and that of a third particle (Charlie)—the particle whose state should be teleported to Bob. Based on the outcome of her measurements, Alice sends a signal to Bob. Bob applies a set of unitary transformations, without knowing the state, to the state of his particle. After these transformations, the state of Bob’s particle is identical to Charlie’s. Note that, during this process, Alice and Bob have no information about the state of Charlie’s particle. This process is probabilistic when implemented with entangled photons and linear optics,2 and means that sometimes Alice’s measurement outcome—that of two particles’ Bell states analysis—is not determined. Thus, Bob does not receive any classical signal, and the teleportation fails. Nevertheless, when Bob receives the signal from Alice, the state is the correct one, and teleportation has succeeded with a 100% fidelity. We can use a single particle possessing two different quantum properties to present a non-separable state, where Figure 1. (a) The setup for remote-hybrid-teleportation of photons from the spin to the orbital-angular-momentum degree of freedom (OAM DOF). A UV laser pumps a barium borate (BBO) crystal to generate photon pairs that are entangled in their OAM DOF. A polarizing Sagnac interferometer containing a dove prism (PSI-DP), shown in the inset, in combination with the half-wave plate (H), spatial light modulator (SLM), bandpass interference filter (IF) and single mode optical fiber (SMF) perform the single photon spin-OAM non-separable Bell state measurement.4 The photons couple via a fiber coupler (FC) into the SMF for detection by an avalanche photodiode (APD). The APD triggers the intensified charge-coupled camera (ICCD) to record the spatial distribution of photon B. During the preparation and measurement of photon A, photon B propagates in the delay line (D), compensating for electronic delay. (b) First and second columns show the polarization (SAM) state of C and the OAM state of the teleported photon to B. jLi, jH i, and jV i: left, horizontal, and vertical polarization, respectively. M: Mirror. PBS: Polarizing beam splitter. TEM: Transverse electromagnetic mode—this refers to the fundamental transverse mode (beam with a Gaussian profile). Q: Quarter-wave plate.