Experimental quantum cryptography with qutrits

Abstract

We produce two identical keys using, for the first time, entangled trinary quantum systems (qutrits) for quantum key distribution. The advantage of qutrits over the normally used binary quantum systems is an increased coding density and a higher security margin. The qutrits are encoded into the orbital angular momentum of photons, namely Laguerre-Gaussian modes with azimuthal index l +1, 0 and −1, respectively. The orbital angular momentum is controlled with phase holograms. In an Ekert-type protocol the violation of a three-dimensional Bell inequality verifies the security of the generated keys. A key is obtained with a qutrit error rate of approximately 10%.

Vortex entanglement in Bose-Einstein condensates coupled to Laguerre-Gauss beams

“…The analytic solution of such a dynamics is a formidable problem, and we thus resort to a numerical investigation in order to infer the behavior of f i (t)s. To find the coefficients {f i (t)}, we have numerically solved the Schrödinger equation using the Hamiltonian in Eqs. (11). 2 We have explored a wide range of parameters, including the case where the system is symmetric under the exchange of the two BECs, finding qualitatively similar results.…”

“…The initial state is thus taken to be | (0) ABαβ = |N A 0 ,N B 0 AB | Z αβ , whose dynamics under Eqs. (11) are now evaluated in a rotating frame defined according to Eq. (A2) (see the appendix).…”

“…It has been shown that it is possible to create OAM-entangled photons by means of a routinely used setup such as spontaneous parametric down-conversion (SPDC) [7]. This has triggered a plethora of studies on how to generate, manipulate, and detect nonclassical states of OAM [8], culminating in the demonstration of Bell's inequality violation by OAM-entangled two-photon states [9], the introduction of so-called hyperentangled states [10], the design of quantum cryptographic schemes based on higherdimensional systems [11], and the transfer of OAM states from light to matterlike systems [12].…”

Orbital-angular-momentum entanglement in turbulence

“…In view of the increased storage capacity per photon and the corresponding new potential quantum communication protocols, OAM entangled photons are candidate carriers for long-range quantum communication [6] and higher dimensional quantum key distribution [7]. So far, protocols to achieve long-range quantum communication are based on the distribution of quantum correlations (entanglement) between the nodes of a network combined with teleportation of these correlations from one node to the next, a process also known as entanglement swapping [8][9][10].…”

Quantum orbital angular momentum of elliptically symmetric light

“…Since the seminal paper by Allen et al [1] research in this field has accelerated. Interest has been driven by the promise of access to higher dimensional Hilbert spaces (especially larger alphabet quantum key distribution [2,3]), potential probes of heretofore hidden phenomena (even astronomical events [4]), metrology [5], use in micro-mechanics [6], and perhaps most importantlythe insight the study of OAM yields into the fundamental properties of light fields themselves. Especially illuminating, is the investigation of the quantum aspects of OAM carrying light modes.…”