Preserving photon qubits in an unknown quantum state with Knill dynamical decoupling: Towards an all optical quantum memory

Abstract

The implementation of polarization-based quantum communication is limited by signal loss and decoherence caused by the birefringence of a single-mode fiber. We investigate the Knill dynamical decoupling scheme, implemented using half-wave plates, to minimize decoherence and show that a fidelity greater than 99% can be achieved in absence of rotation error and fidelity greater than 96% can be achieved in presence of rotation error. Such a scheme can be used to preserve any quantum state with high fidelity and has potential application for constructing all optical quantum delay line, quantum memory, and quantum repeater.

High precision Optical AC Magnetometry using Dynamical Decoupling

“…A technique for minimizing the quantum noise is called dynamical decoupling. The application of dynamical decoupling in an optical fiber to reduce quantum noise was first proposed by Wu and Lidar in [22], and later investigated in [23][24][25][26][27] for the protection of photonic qubits traveling in an optical fiber. Although dynamical decoupling has been used to preserve the state of a qubit, it has never been applied for reduction of noise in an AC signal in an optical fiber.…”

“…If a photonic qubit propagates for a length ∆L in an optical fiber then the phase accumulated by it is given by ∆φ = (2π/λ)∆L∆n, where ∆n is the birefringence of the fiber and λ is the wavelength. We model the axially varying index dephasing in an optical fiber of length L by a series of concatenated, homogeneous segments of length ∆L with constant ∆n [23,26,31]. The index fluctuations across these segments of fiber are random and the stochastic fluctuation of refractive index difference ∆n(x) across the segments are simulated as a Gaussian-distributed zero mean random process [31,32].…”

Dephasing of Single-Photon Orbital Angular Momentum Qudit States in Fiber: Limits to Correction via Dynamical Decoupling

“…In general, the index of refraction fluctuation in an optical fiber can be represented by a series of concatenated, homogeneous segments of length ∆L with constant index fluctuation ∆β = ω(n l −n −l ) c [17,18]. When a photon that is in superposition of +l and −l propagates through the fiber in z direction the E-fields see a slightly different refractive index due to the corkscrew nature of the OAM photon.…”

“…Since the mean of variance is zero in Eq. 10, and average of the variance is ∆ φ2 = ∆φ 2 , hence we obtain the expression [17,19] exp…”

“…Decoherence of a photonic state has its origin in optical index fluctuation of a fiber that can result from both intrinsic and extrinsic perturbations. We model axially varying index dephasing in an optical fiber of length L by a series of concatenated, homogeneous segments of length ∆L with constant ∆n [17,18,20]. The index fluctuations across these segments is modeled by generating a set of values according to the Rayleigh distribution, whose probability density function is given as…”