arXiv subjects

Andon A. Rangelov

Publications and source records attributed to Andon A. Rangelov.

18 recordsLinked to original sources

arXiv2026

Universal composite phase gates with tunable target phase

We present a systematic method for constructing universal composite phase gates with a continuously tunable target phase. Using a general Cayley--Klein parametrization of the single-pulse propagator, we design gates from an even number of nominal $π$ pulses and derive analytic phase families by canceling, order by order in a small deviation parameter, the leading contributions to the undesired off-diagonal element of the composite propagator, independently of the dynamical phase. The resulting sequences provide intrinsic robustness against generic control imperfections and parameter fluctuations and remain valid for arbitrary pulse shapes. Numerical simulations in a standard two-level model confirm high-order error suppression and demonstrate broad, flat high-fidelity plateaus over wide ranges of simultaneous pulse-area and detuning errors, highlighting the efficiency of the proposed universal composite phase gates for resilient phase control in quantum information processing.

quant-ph↗

arXiv2025

Robust population transfer by a detuning sign jump: from two-state quantum system to SU(2)-symmetric three-state quantum system

We propose and analyze a robust population-transfer protocol in a driven two-level system based on a sudden sign change of the detuning at the maximum of a smooth coupling pulse. Away from the jump the dynamics is adiabatic, while the sign flip produces a single nonadiabatic kick in the adiabatic basis. Within a simple stepwise adiabatic-sudden approximation we obtain a compact analytic expression for the final transition probability, identify the parameter regimes that yield high-fidelity inversion, and show that the result depends only on the change of the mixing angle across the detuning jump, i.e., solely on the ratio of the peak Rabi frequency to the detuning. Numerical simulations of the full time-dependent Schrödinger equation confirm the validity and robustness of this description over a broad parameter range. We then use the Majorana decomposition to extend the scheme to an SU(2)-symmetric three-state chain driven by the same coupling and detuning functions. In this setting the three-state propagator is expressed in closed form through the two-level Cayley-Klein parameters, which allows us to derive explicit transition probabilities for all three initial states. In particular, we show that for strong coupling the protocol yields almost complete population transfer between the two outer states, with only small transient population of the middle state, while retaining the same intrinsic robustness as in the underlying two-level model.

quant-ph↗

arXiv2025

Complete and robust population transfer between the two ground states of a three-state loop quantum system by amplitude composite pulse control

This work presents a method for achieving complete, robust, and efficient population transfer between the two ground states in a three-level loop quantum system. The approach utilizes composite pulse sequences by effectively mapping the three-state system onto an equivalent two-level system. This transformation allows the use of broadband composite pulses designed initially for conventional two-state quantum systems. Unlike traditional implementations, the composite pulses in the three-level system are not controlled through phase adjustments; instead, they are realized via the amplitude ratio of the Rabi frequencies.

quant-ph↗

arXiv2025

Arbitrary polarization retarders and polarization controllers, constructed from sequences of half-wave and quarter-wave plates

We theoretically introduce several types of arbitrary polarization retarders constructed from sequences of half-wave and quarter-wave plates, each rotated at specific angles. By integrating these arbitrary polarization retarders with arbitrary polarization rotators, we develop a versatile device capable of performing arbitrary-to-arbitrary polarization transformations. While some of the proposed devices are documented in the literature, others are novel and, to the best of our knowledge, have not been previously presented. The continuous adjustment of retardance and rotation in these devices is achieved by altering the relative orientation of the wave plates in the sequence.

physics.optics↗

arXiv2024

Tunable broadband polarization retarders

We theoretically propose a type of tunable polarization retarder, which is composed of sequences of half-wave and quarter-wave polarization retarders, allowing operation at broad spectral bandwidth. The constituent retarders are composed of stacked standard half-wave retarders and quarter-wave retarders rotated at designated angles relative to their fast-polarization axes. The proposed composite retarder can be tuned to an arbitrary value of the retardance by varying the middle retarder alone, while maintaining its broadband spectral bandwidth intact.

physics.optics↗

arXiv2024

Creation of coherent superpositions of Raman qubits by using dissipation

We show how to create coherent superpositions between two ground states of Lamda quantum system of three states, among which the middle one decays. The idea is to deplete the population of the bright state formed by the two ground states via the population loss channel. The remaining population is trapped in the dark states, which can be designed to be equal to any desired coherent superposition of the ground states. The present concept is an alternative to the slow adiabatic creation of coherent superpositions and may therefore be realized over short times, especially in the case where the middle state has a short life span. However, the price we pay for the fast evolution is associated with an overall 50% population losses. This issue can be removed in an experiment by using post-selection.

quant-ph↗

arXiv2023

Broadband composite nonreciprocal polarization wave plates and optical isolators

We provide a technique for a broadband nonreciprocal wave retarder whose quarter-wave plate phase retardation is the same in forward and backward directions. The system is built using a number of sequential nonreciprocal wave plates. The proposed device can also be utilized to create a broadband optical diode, which consists of two achromatic quarter-wave plates, one reciprocal and the other non-reciprocal, that are sandwiched between two polarizers aligned in parallel.

physics.optics↗

arXiv2021

Ultrabroadband beam splitting in a dissipative system of three waveguides

We show that a system of three parallel waveguides, among which the central one is dissipative, leads to an ultrabroadband power splitting associated with an overall 50% power loss. The present approach is reminiscent of non-Hermitian systems in quantum mechanics and does not require a perfect effective index matching between the external and the central waveguides. The present concept does not need any slow adiabatic evolution of the waveguide parameters and may therefore be realized over very short device lengths, especially in the case where the central waveguide is of the plasmonic type.

physics.optics↗

arXiv2016

Stimulated Raman adiabatic passage in physics, chemistry and beyond

The technique of stimulated Raman adiabatic passage (STIRAP), which allows efficient and selective population transfer between quantum states without suffering loss due to spontaneous emission, was introduced in 1990 (Gaubatz \emph{et al.}, J. Chem. Phys. \textbf{92}, 5363, 1990). Since then STIRAP has emerged as an enabling methodology with widespread successful applications in many fields of physics, chemistry and beyond. This article reviews the many applications of STIRAP emphasizing the developments since 2000, the time when the last major review on the topic was written (Vitanov \emph{et al.}, Adv. At. Mol. Opt. Phys. \textbf{46}, 55, 2001). A brief introduction into the theory of STIRAP and the early applications for population transfer within three-level systems is followed by the discussion of several extensions to multi-level systems, including multistate chains and tripod systems. The main emphasis is on the wide range of applications in atomic and molecular physics (including atom optics, cavity quantum electrodynamics, formation of ultracold molecules, precision experiments, etc.), quantum information (including single- and two-qubit gates, entangled-state preparation, etc.), solid-state physics (including processes in doped crystals, nitrogen-vacancy centers, superconducting circuits, etc.), and even some applications in classical physics (including waveguide optics, frequency conversion, polarization optics, etc.). Promising new prospects for STIRAP are also presented (including processes in optomechanics, detection of parity violation in molecules, spectroscopy of core-nonpenetrating Rydberg states, and population transfer with X-ray pulses).

quant-ph↗

arXiv2014

Broadband composite polarization rotator

We describe a broadband optical device that is capable of rotating the polarization plane of a linearly polarized light at any desired angle over a wide range of wavelengths. The device is composed of a sequence of half-wave plates rotated at specific angles with respect to their fast-polarization axes. This design draws on an analogy with composite pulses, which is a well-known control technique from quantum physics. We derive the solutions for the rotation angles of the single half-wave plates depending on the desired polarization rotation angle. We show that the broadband polarization rotator is robust against variations of the parameters of both the crystal and the light field.

physics.optics↗

arXiv2014

Complete achromatic optical switching between two waveguides with a sign flip of the phase mismatch

We present a two-waveguide coupler which, realizes complete achromatic all-optical switching. The coupling of the waveguides has a hyperbolic-secant shape while the phase mismatch has a sign flip at the maximum of the coupling. We derive an analytic solution for the electric field propagation using coupled mode theory and show that the light switching is robust again small-to-moderate variations in the coupling and phase mismatch. Thus, we realize an achromatic light switching between the two waveguides. We further consider the extended case of three coupled waveguides in an array and pay special attention to the case of equal achromatic light beam splitting.

quant-ph↗

arXiv2013

Broadband optical isolator in fibre optics

We propose a broadband optical diode, which is composed of one achromatic reciprocal quarter-wave plate and one non-reciprocal quarter-wave plate, both placed between two crossed polarizers. The presented design of achromatic wave plates relies on an adiabatic evolution of the Stokes vector, thus, the scheme is robust and efficient. The possible simple implementation using fiber optics is suggested.

physics.optics↗

arXiv2012

Variable Ultra-broadband and Narrowband Composite Polarization Retarders

We propose and experimentally demonstrate novel types of composite sequences of half-wave and quarter-wave polarization retarders, either permitting operation at ultra-broad spectral bandwidth or narrow bandwidth. The retarders are composed of stacked standard half-wave retarders and quarter-wave retarders of equal thickness. To our knowledge, these home-built devices outperform all commercially available compound retarders, made of several birefringent materials.

physics.optics↗

arXiv2012

Broadband Faraday Isolator

Driving on an analogy with the technique of composite pulses in quantum physics, we propose a broadband Faraday rotator and thus a broadband optical isolator, which is composed of sequences of ordinary Faraday rotators and achromatic quarter-wave plates rotated at the predetermined angles.

physics.optics↗

arXiv2012

Achromatic multiple beam splitting by adiabatic passage in optical waveguides

A novel variable achromatic optical beam splitter with one input and $N$ output waveguide channels is introduced. The physical mechanism of this multiple beam splitter is adiabatic passage of light between neighboring optical waveguides in a fashion reminiscent of the technique of stimulated Raman adiabatic passage in quantum physics. The input and output waveguides are coupled via a mediator waveguide and the ratios of the light intensities in the output channels are controlled by the couplings of the respective waveguides to the mediator waveguide. Due to its adiabatic nature the beam splitting efficiency is robust to variations in the experimental parameters.

physics.optics↗

arXiv2012

Efficient broadband sum and difference frequency generation with a single chirped quasi-phase-matching crystal

We propose an efficient broadband frequency generation technique for two collinear optical parametric processes $ω_3=ω_1+ω_2$ and $ω_4=ω_1-ω_2$. It exploits chirped quasi-phase-matched gratings, which in the undepleted pump approximation regime perform population transfer that is analogous to adiabatic population transfer in a three-state ``vee'' quantum system. The energy of the input fields is transferred adiabatically either into $ω_3$ or $ω_4$ field, depending on which of the two phase matchings occurs first by the local modulation period in the crystal. One can switch the output between $ω_3$ and $ω_4$ by inverting the direction of the local modulation sweep, which corresponds to a rotation of the crystal by angle $π$

physics.optics↗

arXiv2012

Mid-range adiabatic wireless energy transfer via a mediator coil

A technique for efficient mid-range wireless energy transfer between two coils via a mediator coil is proposed. By varying the coil frequencies three resonances are created: emitter-mediator (EM), mediator-receiver (MR) and emitter-receiver (ER). If the frequency sweeps are adiabatic and such that the ER resonance precedes the MR resonance, the energy flows sequentially along the chain emitter-mediator-receiver. If the MR resonance precedes the ER resonance, then the energy flows directly from the emitter to the receiver via the ER resonance; then the losses from the mediator are suppressed. This technique is robust to noise, resonant constraints and external interferences.

physics.atom-ph↗

arXiv2012

Complete population transfer in a three-state quantum system by a train of pairs of coincident pulses

A technique for complete population transfer between the two end states $\ket{1}$ and $\ket{3}$ of a three-state quantum system with a train of $N$ pairs of resonant and coincident pump and Stokes pulses is introduced. A simple analytic formula is derived for the ratios of the pulse amplitudes in each pair for which the maximum transient population $P_2(t)$ of the middle state $\ket{2}$ is minimized, $P_2^{\max}=\sin^2(π/4N)$. It is remarkable that, even though the pulses are on exact resonance, $P_2(t)$ is damped to negligibly small values even for a small number of pulse pairs. The population dynamics resembles generalized $π$-pulses for small $N$ and stimulated Raman adiabatic passage for large $N$ and therefore this technique can be viewed as a bridge between these well-known techniques.

quant-ph↗