Spin-orbit Modes Research Articles

Transition from quantum to classical random walk distributions with spin-orbit modes

Transition from quantum to classical random walk distributions with spin-orbit modes

Integrated preparation and manipulation of high-dimensional flying structured photons

The hope for a futuristic global quantum internet that provides robust and high-capacity quantum information transfer lies largely on qudits, the fundamental quantum information carriers prepared in high-dimensional superposition states. However, preparing and manipulating N-dimensional flying qudits as well as subsequently establishing their entanglement are still challenging tasks, which require precise and simultaneous maneuver of 2 (N-1) parameters across multiple degrees of freedom. Here, using an integrated approach, we explore the synergy from two degrees of freedom of light, spatial mode and polarization, to generate, encode, and manipulate flying structured photons and their formed qudits in a four-dimensional Hilbert space with high quantum fidelity, intrinsically enabling enhanced noise resilience and higher quantum data rates. The four eigen spin–orbit modes of our qudits possess identical spatial–temporal characteristics in terms of intensity distribution and group velocity, thereby preserving long-haul coherence within the entirety of the quantum data transmission link. Judiciously leveraging the bi-photon entanglement, which is well preserved in the integrated manipulation process, we present versatile spin–orbit cluster states in an extensive dimensional Hilbert space. Such cluster states hold the promise for quantum error correction which can further bolster the channel robustness in long-range quantum communication.

Quantum phase gates with geometric phases of spin-orbit modes

Quantum phase gates with geometric phases of spin-orbit modes

Theory of four wave mixing-based parametric amplification of spin-orbit modes.

We study the generation of spin-orbit (SO) modes via four-wave mixing (FWM)-based parametric amplification. SO modes carry quantized total angular momentum (TAM), and we show that FWM processes that generate new signals conserve TAM. This is a generalization of prior research which operated in a regime where FWM processes conserved spin and orbital angular momenta independently. We calculate the growth rates of new modes for both degenerate and nondegenerate pump configurations. Our theory is validated against numerical simulations for the cases where the generated signals are in the same SO mode(s) as the pump(s). We also calculate the growth rates of signals in SO modes other than the pumps.

Non-separability classification of degrees of freedom of light assisted by machine learning

In this work, we present a study about the non-separability of degrees of freedom (DoF) of light in mixed modes, which emulates entangled mixed states. We explore bipartite spin–orbit modes and, by adding path DoF to spin–orbit modes, we propose an optical circuit to prepare tripartite non-separable mixed modes that extend the scenario of the classical-quantum analogy of non-separable modes. By using Machine Learning it was possible to show that we can characterize non-separability unambiguously with partial tomography measurements only on Sz basis, which is a remarkable advantage for higher dimension modes avoiding many tomographic measurements.

Partial nonseparability of spin-orbit modes

Structured light plays an essential role in several quantum information protocols by using the degrees of freedom of light to encode qubits. For exploring different correlations, especially in mixed states, such as discord, it is necessary to prepare partially entangled states. In this work, we present a theoretical and experimental study of a partial nonseparable spin-orbit modes. By exploring classical-quantum analogy, we perform the measurement of the concurrence of partially separable modes directly from projective measurement of polarization. The results show a clear agreement with predictions of quantum theory for partially entangled states. We also perform a study of Clauser, Horn, Shimony, and Holt (CHSH) inequality and show that partial violation is observed in entire agreement with the expected by quantum theory. For the maximally nonseparable mode, we achieve a violation of , one of the higher ones observed for spin-orbit modes based on our best knowledge.

Spin-orbit X states

We propose an all-optical setup to produce a wide class of $X$ states with an intense laser beam using spin-orbit modes. In order to characterize such simulated states, we reconstructed the density matrix by simulating spin-orbit tomography and studied the discord and concurrence for different states. The results show very good agreement with theoretical predictions. We also propose two different optical circuits to prepare the single-photon spin-orbit $X$ state.

Classical analog of quantum contextuality in spin-orbit laser modes

We experimentally observed the violation of Kujula-Dzhafarov noncontextuality inequalities by non-separable spin-orbit laser modes. Qubits are encoded on polarization and transverse modes of an intense laser beam. A spin-orbit non-separable mode was produced by means of a radial polarization converter (S-plate). The results show that contextuality can be investigated by using spin-orbit modes in a simple way, corroborating recent works stating that such system can emulate single-photon experiments. Additionally, an improvement in the non-separable mode preparation allowed us to observe a greater violation of the Clauser-Horne-Shimony-Holt inequality for such system. The results are in very good agreement with the theoretical predictions of quantum mechanics.

Quantum and classical separability of spin-orbit laser modes

In this work we investigate the quantum noise properties of polarization vortices in connection with an intensity based Clauser-Horne-Shimony-Holt inequality for their spin-orbit separability. We evaluate the inequality for different input quantum states and the corresponding intensity fluctuations. The roles played by coherence and photon number squeezing provide a suitable framework for characterizing pure state spin-orbit entanglement. Structural inseparability of the spin-orbit mode requires coherence, an issue concerning either classical or quantum descriptions. In both cases, it can be witnessed by violation of this intensity based CHSH inequality. However, in the quantum domain, entanglement requires both coherence and reduced photon number fluctuations.

Topological phase structure of vector vortex beams.

The topological phase acquired by vector vortex optical beams is investigated. Under local unitary operations on their polarization and transverse degrees of freedom, the vector vortices can only acquire discrete geometric phase values, 0 or π, associated with closed paths belonging to different homotopy classes on the SO(3) manifold. These discrete values are demonstrated through interferometric measurements, and the spin-orbit mode separability is associated to the visibility of the interference patterns. The local unitary operations performed on the vector vortices involved both polarization and transverse mode transformations with birefringent wave plates and astigmatic mode converters. The experimental results agree with our theoretical simulations and generalize our previous results obtained with polarization transformations only.

Magnetization and Collective Excitations of a Magnetic Dipole Fermion Gas

The ground states of trapped Fermion gases consisting of atoms with magnetic dipole moment are studied using the time-dependent Hartee–Fock approximation (TDHFA). We also study the effects of quantum fluctuations using the time-dependent density-matrix approach (TDDMA). It was shown that the magnetization associated with the instability against the Rashba like spin–orbit mode realizes first and that such magnetization can occur independently of the number of atoms \(N\). Comparison with the exact solutions given in the TDDMA for an \(N=2\) system suggests that the instabilities given by the Hartree–Fock approximation are shifted to stronger interaction regimes due to quantum fluctuations. It is also pointed out that the tensor properties of the dipole–dipole interaction can be revealed in the excitations associated with spin degrees of freedom.

Spin–orbit mode selection with a modified Sagnac interferometer

We report on a modified Sagnac interferometer used to sort spin–orbit modes of a paraxial beam. The interferometer works as a parity sorter and can be useful for quantum information protocols. The geometry used benefits from phase stability and allows for independent manipulation of the interfering beams.

Comblike entangled spectrum for composite spin-orbit modes from hyperconcentration

I propose a practical scheme of hyperconcentration, by which two-qubit photon spin and two-qudit orbital angular momentum (OAM) maximally entangled states can be distilled simultaneously. The original nonmaximally hyperentangled photon pairs are generated by parametric down conversion and the symmetrical procrustean concentration is then performed using pairs of spatial light modulators (operating on OAM) and partial polarizing interferometers (operating on spin). Furthermore, I show that a generalized Shannon dimensionality can be introduced to evaluate the performance, which is maximized with the formation of a comblike entangled spectrum for composite spin-orbit modes. The results hold promise for ultrahigh-dimensional quantum-information processing.

Bell-like inequality for the spin-orbit separability of a laser beam

In analogy with Bell's inequality for two-qubit quantum states we propose an inequality criterion for the non-separability of the spin-orbit degrees of freedom of a classical laser beam. A definition of separable and non-separable spin-orbit modes is used in consonance with the one presented in Phys. Rev. Lett. 99, 160401 (2007). As the usual Bell's inequality can be violated for entangled two-qubit quantum states, we show both theoretically and experimentally that the proposed spin-orbit inequality criterion can be violated for non-separable modes. A discussion on the classical-quantum transition is also presented.