Nikola Šibalić
Durham University
Network
Latest external collaboration on country level. Dive into details by clicking on the dots.
Publication
Featured researches published by Nikola Šibalić.
Nature Photonics | 2017
Christopher G. Wade; Nikola Šibalić; N. R. de Melo; Jorge M. Kondo; C. S. Adams; K. J. Weatherill
A time-averaged intensity distribution of terahertz waves is imaged by converting terahertz waves to optical fluorescence. The conversion becomes possible by exciting Cs atoms to a Rydberg state. The image acquisition time is 40 ms. Terahertz (THz) near-field imaging is a flourishing discipline1,2, with applications from fundamental studies of beam propagation3 to the characterization of metamaterials4,5 and waveguides6,7. Beating the diffraction limit typically involves rastering structures or detectors with length scale shorter than the radiation wavelength; in the THz domain this has been achieved using a number of techniques including scattering tips8,9 and apertures10. Alternatively, mapping THz fields onto an optical wavelength and imaging the visible light removes the requirement for scanning a local probe, speeding up image collection times11,12. Here, we report THz-to-optical conversion using a gas of highly excited Rydberg atoms. By collecting THz-induced optical fluorescence we demonstrate a real-time image of a THz standing wave and use well-known atomic properties to calibrate the THz field strength.
Computer Physics Communications | 2017
Nikola Šibalić; J. D. Pritchard; C. S. Adams; K. J. Weatherill
Abstract We present an object-oriented Python library for the computation of properties of highly-excited Rydberg states of alkali atoms. These include single-body effects such as dipole matrix elements, excited-state lifetimes (radiative and black-body limited) and Stark maps of atoms in external electric fields, as well as two-atom interaction potentials accounting for dipole and quadrupole coupling effects valid at both long and short range for arbitrary placement of the atomic dipoles. The package is cross-referenced to precise measurements of atomic energy levels and features extensive documentation to facilitate rapid upgrade or expansion by users. This library has direct application in the field of quantum information and quantum optics which exploit the strong Rydberg dipolar interactions for two-qubit gates, robust atom-light interfaces and simulating quantum many-body physics, as well as the field of metrology using Rydberg atoms as precise microwave electrometers. Program summary Program Title: ARC: Alkali Rydberg Calculator Program Files doi: http://dx.doi.org/10.17632/hm5n8w628c.1 Licensing provisions: BSD-3-Clause Programming language: Python 2.7 or 3.5, with C extension External Routines: NumPy [1], SciPy [1], Matplotlib [2] Nature of problem: Calculating atomic properties of alkali atoms including lifetimes, energies, Stark shifts and dipole–dipole interaction strengths using matrix elements evaluated from radial wavefunctions. Solution method: Numerical integration of radial Schrodinger equation to obtain atomic wavefunctions, which are then used to evaluate dipole matrix elements. Properties are calculated using second order perturbation theory or exact diagonalisation of the interaction Hamiltonian, yielding results valid even at large external fields or small interatomic separation. Restrictions: External electric field fixed to be parallel to quantisation axis. Supplementary material: Detailed documentation (.html), and Jupyter notebook with examples and benchmarking runs (.html and .ipynb). [1] T.E. Oliphant, Comput. Sci. Eng. 9, 10 (2007). http://www.scipy.org/ . [2] J.D. Hunter, Comput. Sci. Eng. 9, 90 (2007). http://matplotlib.org/ .
Physical Review A | 2016
Nikola Šibalić; Christopher G. Wade; C. S. Adams; K. J. Weatherill; Thomas Pohl
We investigate the nonequilibrium dynamics of a driven-dissipative spin ensemble with competing power-law interactions. We demonstrate that dynamical phase transitions as well as bistabilities can emerge for asymptotic van der Waals interactions, but critically rely on the presence of a slower decaying potential core. Upon introducing random particle motion, we show that a finite gas temperature can drive a phase transition with regards to the spin degree of freedom and eventually leads to mean-field behavior in the high-temperature limit. Our work reconciles contrasting observations of recent experiments with Rydberg atoms in the cold-gas and hot-vapor domain, and introduces an efficient theoretical framework in the latter regime.
Physical Review Letters | 2017
Daniel J. Whiting; Nikola Šibalić; James Keaveney; C. S. Adams; Ifan G. Hughes
We experimentally demonstrate the heralded generation of bichromatic single photons from an atomic collective spin excitation (CSE). The photon arrival times display collective quantum beats, a novel interference effect resulting from the relative motion of atoms in the CSE. A combination of velocity-selective excitation with strong laser dressing and the addition of a magnetic field allows for exquisite control of this collective beat phenomenon. The present experiment uses a diamond scheme with near-IR photons that can be extended to include telecommunications wavelengths or modified to allow storage and retrieval in an inverted-Y scheme.
Physical Review A | 2016
Natalia R. de Melo; Christopher G. Wade; Nikola Šibalić; Jorge M. Kondo; C. S. Adams; K. J. Weatherill
We observe and characterize intrinsic optical bistability in a dilute Rydberg vapor. The bistability is characterized by sharp jumps between states of low and high Rydberg occupancy with jump-up and -down positions displaying hysteresis depending on the direction in which the control parameter is changed. We find that the shift in frequency of the jump point scales with the fourth power of the principal quantum number. Also, the width of the hysteresis window increases with increasing principal quantum number, before reaching a peak and then closing again. The experimental results are consistent with predictions from a simple theoretical model based on semiclassical Maxwell--Bloch equations including the effects of interaction-induced broadening and level shifts. These results provide insight into the dynamics of driven dissipative systems.
Physical Review A | 2016
Nikola Šibalić; Jorge M. Kondo; C. S. Adams; K. J. Weatherill
We present, experimentally and theoretically, a scheme for dressed-state electromagnetically induced transparency (EIT) in a three-step cascade system in which a four-level system is mapped into an effective three-level system. Theoretical analysis reveals that the scheme provides coherent-state control via adiabatic following and a generalized protocol for light storage in uniform phase spin-waves that are insensitive to motional dephasing. The three-step driving enables a number of other features, including spatial selectivity of the excitation region within the atomic medium, and kick-free and Doppler-free excitation that produces narrow resonances in thermal vapor. As a proof of concept, we present an experimental demonstration of the generalized EIT scheme using the 6S1/2→6P3/2→7S1/2→8P1/2 excitation path in thermal cesium vapor. This technique could be applied to cold and thermal ensembles to enable longer storage times for Rydberg polaritons.
Physical Review A | 2014
Christopher G. Wade; Nikola Šibalić; James Keaveney; C. S. Adams; K. J. Weatherill
We describe a method to observe the dynamics of an excited-state transition in a room-temperature atomic vapor using hyperfine quantum beats. Our experiment using cesium atoms consists of a pulsed excitation of the D2 transition and continuous-wave driving of an excited-state transition from the 6P3/2 state to the 7S1/2 state. We observe quantum beats in the fluorescence from the 6P3/2 state which are modified by the driving of the excited-state transition. The Fourier spectrum of the beat signal yields evidence of Autler-Townes splitting of the 6P3/2, F=5 hyperfine level and Rabi oscillations on the excited-state transition. A detailed model provides qualitative agreement with the data, giving insight to the physical processes involved.
Optics Letters | 2015
Jorge M. Kondo; Nikola Šibalić; Guttridge A; Christopher G. Wade; De Melo Nr; C. S. Adams; K. J. Weatherill
We report on the observation of electromagnetically induced transparency (EIT) and absorption (EIA) of highly excited Rydberg states in thermal Cs vapor using a four-step excitation scheme. The advantage of this four-step scheme is that the final transition to the Rydberg state has a large dipole moment and one can achieve similar Rabi frequencies to two- or three-step excitation schemes using two orders of magnitude less laser power. This scheme enables new applications such as dephasing free Rydberg excitation. The observed lineshapes are in good agreement with simulations based on multilevel optical Bloch equations.
Frontiers in Optics | 2017
Natalia R. de Melo; Christopher G. Wade; Nikola Šibalić; Jorge M. Kondo; C. S. Adams; K. J. Weatherill
Bulletin of the American Physical Society | 2016
Christopher G. Wade; Nikola Šibalić; Jorge M. Kondo; Natalia R. de Melo; C. S. Adams; K. J. Weatherill