The Depolarizing channel is one of the most important noise models and constitutes a reliable benchmark for the quantum information field. In this work, we present a simple way to emulate a Depolarizing channel by exploring a maximally non separable spin-orbit mode in a compact linear optical circuit. The evolution of different states has been successfully reproduced. Our results are in excellent agreement compared with the results obtained by the spin-orbit Solovay-Kitaev decomposition for the Depolarizing channel, also presented here for the first time. Our proposal can be a powerful tool for studies of depolarizing effect.
The Depolarizing channel is one of the most important noise models and constitutes a reliable benchmark for the quantum information field. In this work, we present a simple way to emulate a Depolarizing channel by exploring a maximally non separable spin-orbit mode in a compact linear optical circuit. The evolution of different states has been successfully reproduced. Our results are in excellent agreement compared with the results obtained by the spin-orbit Solovay-Kitaev decomposition for the Depolarizing channel, also presented here for the first time. Our proposal can be a powerful tool for studies of depolarizing effect.
The Solovay-Kitaev theorem allows us to approximate any single-qubit gate to arbitrary accuracy with a finite sequence of fundamental operations from a universal set of gates. Inspired by this decomposition, we present a quantum channel simulator capable of implementing any completely positive trace-preserving map. Our realization consists of one ancillary qubit, encoded in the transverse mode of a laser beam (orbital degree of freedom), one qubit system, encoded in its polarization (spin), one spin-orbit CNOT gate, and four single-qubit operations performed with prisms and polarization components. Our results describe the implementation of arbitrary single-qubit channels on the photon polarization using the transverse mode as the ancillary qubit.
We introduce a proposal to prepare spin-obit maximally discordant mixed states by a linear optical circuit, with quantum bits (qubits) encoded in the polarization and transverse mode degrees of freedom of photons. In particular, we discuss how to prepare nonbalanced spin-orbit entangled states, applying this technique to obtain maximally discordant mixed states. We present a simulation of the optical circuit by using the Jones matrix formalism. We performed a study of entanglement, classical, and quantum correlations. The results show excellent agreement with the underlying theory and open an alternative experimental approach for addressing quantum correlations in optical setups.
Quantum walks (QW) offer a speed-up advantage over random walks in quantum search applications. We present an experimental study of the transition from quantum-to-classical random walk using an emulation of the decoherence process for polarization qubits that exploits maximally non-separable spin-orbit modes of an intense laser beam for the first, to the best of our knowledge, time. We are able to continuously control the input polarization mode in an all-optical quantum walk circuit to observe transitions associated with quantum, quantum stochastic, and classical random walk distributions. The results are in agreement with theoretical expectations.
Abstract 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 S = 2.73 ± 0.03 , one of the higher ones observed for spin-orbit modes based on our best knowledge.
The observation of extreme dynamics within quantum simulators based on photonic circuits is typically precluded by optical losses, exponentially increasing with the system depth or, equivalently, with the number of optical components. This is a natural consequence of the standard approach to photonic simulations of quantum dynamics, where the complexity of the setup grows with the extension of the evolution in time. By focusing on simple protocols of discrete-time quantum walks, we show that it is possible to compress homogeneous evolutions within only three liquid-crystal metasurfaces, encompassing up to a few hundreds of time steps. By exploiting spin-orbit effects, these devices implement space-dependent polarization transformations that mix circularly polarized optical modes carrying quantized transverse momentum, mimicking the target quantum dynamics with high efficiency and accuracy. Being extremely versatile, our compact platform will pave the way to the simulations of extreme regimes of more exotic dynamics.
A major problem in exploiting microscopic systems for developing a new technology based on the principles of quantum information is the influence of noise, which tends to work against the quantum features of such systems. It thus becomes crucial to understand how noise affects the evolution of quantum circuits: several techniques have been proposed, among which stochastic differential equations (SDEs) can represent a very convenient tool. We show how SDEs naturally map any Markovian noise into a linear operator, which we call a noise gate, acting on the wave function describing the state of the circuit, and we discuss some examples. We show that these gates can be manipulated like any standard quantum gate, thus simplifying in certain circumstances the task of computing the overall effect of the noise at each stage of the protocol. This approach yields equivalent results to those derived from the Lindblad equation; yet, as we show, it represents a handy and fast tool for performing computations, and, moreover, it allows for fast numerical simulations and generalizations to non-Markovian noise. In detail we review the depolarizing channel and the generalized amplitude damping channel in terms of this noise gate formalism and show how these techniques can be applied to any quantum circuit.