Entanglement of the orbital angular momentum states of photons

Abstract

Entanglement contains one of the most interesting features of quantum mechanics, often named quantum non-locality [1,2]. This means entangled states are not separable regardless of the spatial separation of their components. Measurement results on one particle of a two-particle entangled state define the state of the other particle instantaneously with neither particle enjoying its own well-defined state before the measurement.So far experimental confirmation of entanglement has been restricted to qubits, i.e. two-state quantum systems including recent realization of three- [3,4] and four-qubit [5,6] entanglements. Yet, an ever increasing body of theoretical work calls for entanglement in quantum system of higher dimensions [7,8]. For photons one is restricted to qubits as long as the entanglement is realized using the photons polarization. Here we report the first realization of entanglement exploiting the orbital angular momentum of photons,

Quantum encodings in spin systems and harmonic oscillators

“…Qubits are obtained by restricting the dynamics to just two of these quanta, namely the vacuum state |0 and the first excited state |1 ; e.g., photons in cavity QED [3] and interferometry [4]. However, the control of entanglement in larger Hilbert spaces is now feasible (e.g., orbital angular momentum states of photons [5]). Our aim is to show that the restriction to two-dimensional Hilbert spaces is not necessary and that higher-dimensional Hilbert spaces are an advantage, particularly when the number of achievable coupled systems is limited and entanglement between systems with larger Hilbert spaces is physically possible.…”

Uhrig dynamical control of a three-level system via non-Markovian quantum state diffusion

“…This new set of control operators only works for ladder-type three-level quantum system with equal distance eigenvalues. Our three-level system represents a spin-1 or angular momentum system which is of interest in many physically interesting case such as quantum cryptography and quantum entanglement [53]. It is interesting to note that a more general three-level system with different energy spacings such as V-type or λ-type atoms, a universal effective control via UUD combined with non-Markovian QSD are still possible, but it becomes much more complicated technically and multi-nesting sequences with different control operators have to be employed.…”

Bell’s Universe: A Personal Recollection

“…One event is unforgettable, when Alois Mair, a student of Anton's group reported on the first experiment of "Entangled states of orbital angular momentum of photons"(published in Ref. [181]). In such states the phase surface of the wave resembled a screw in direction of the wave propagation.…”