Journal Articleshttps://repository.iitgn.ac.in/handle/123456789/6122021-03-08T13:15:13Z2021-03-08T13:15:13ZThe multi-faceted inverted harmonic oscillator: Chaos and complexityBhattacharyya, ArpanChemissany, WissamHaque, S. ShajidulMurugan, JeffYan, Binhttps://repository.iitgn.ac.in/handle/123456789/63292021-03-06T15:08:13Z2021-02-01T00:00:00ZThe multi-faceted inverted harmonic oscillator: Chaos and complexity
Bhattacharyya, Arpan; Chemissany, Wissam; Haque, S. Shajidul; Murugan, Jeff; Yan, Bin
The harmonic oscillator is the paragon of physical models; conceptually and computationally simple, yet rich enough to teach us about physics on scales that span classical mechanics to quantum field theory. This multifaceted nature extends also to its inverted counterpart, in which the oscillator frequency is analytically continued to pure imaginary values. In this article we probe the inverted harmonic oscillator (IHO) with recently developed quantum chaos diagnostics such as the out-of-time-order correlator (OTOC) and the circuit complexity. In particular, we study the OTOC for the displacement operator of the IHO with and without a non-Gaussian cubic perturbation to explore genuine and quasi scrambling respectively. In addition, we compute the full quantum Lyapunov spectrum for the inverted oscillator, finding a paired structure among the Lyapunov exponents. We also use the Heisenberg group to compute the complexity for the time evolved displacement operator, which displays chaotic behaviour. Finally, we extended our analysis to N-inverted harmonic oscillators to study the behaviour of complexity at the different timescales encoded in dissipation, scrambling and asymptotic regimes.
2021-02-01T00:00:00ZEvidence for the significant differences in response times of equatorial ionization anomaly crest corresponding to plasma fountains during daytime and post?sunset hoursKumar, AnkitChakrabarty, D.Pandey, K.Fejer, B. G.Sunda, S.Seemala, G. K.Sripathi, S.Yadav, A. Khttps://repository.iitgn.ac.in/handle/123456789/63182021-02-23T15:40:09Z2021-04-01T00:00:00ZEvidence for the significant differences in response times of equatorial ionization anomaly crest corresponding to plasma fountains during daytime and post?sunset hours
Kumar, Ankit; Chakrabarty, D.; Pandey, K.; Fejer, B. G.; Sunda, S.; Seemala, G. K.; Sripathi, S.; Yadav, A. K
Based on 10 years� (2010?2019) of vertical total electron content (VTEC) data from Ahmedabad (23.0�N, 72.6�E, dip angle 35.2�) and campaign based OI 630.0 nm airglow intensity measurements from Mt. Abu (24.6�N, 72.7�E, dip angle 38.0�), it is shown that plasma density over the equatorial ionization anomaly (EIA) crest region increases in varying degrees during post?sunset hours (2000?2100 LT) in magnetically quiet periods. The post?sunset peak in VTEC precedes the corresponding peak in airglow intensity. By comparing post?sunset VTEC enhancements with ionosonde observations from Tirunelveli (8.7�N, 77.7�E, dip angle 1.7�), it is shown that pre?reversal enhancement (PRE) of the zonal electric field causes these enhancements over the EIA crest region. These observations are supported by TEC measurements by GAGAN (GPS Aided Geo Augmented navigation), the Indian Satellite based Augmentation System (SBAS). Comparison of average VTEC variations with global empirical model drifts reveals that the post?sunset enhancements in VTEC occurs ?1.7 hrs after the PRE and are significant only during December solstice and equinoctial months in high solar activity years similar to seasonal variations in PRE amplitudes. This time delay (response time of EIA crest) is almost half compared to the average response time (3?4 hrs) associated with the daytime fountain. Based on the latitudinal gradient in SBAS?TEC, it is proposed that the PRE drives plasma from 5�?10�N magnetic latitudes to the EIA crest region leading to shorter response time. These results show the important role of the PRE in conditioning the EIA crest region.
2021-04-01T00:00:00ZDynamics of the creation of a rotating Bose Einstein condensation by two photon Raman transition using a Laguerre Gaussian laser pulseMukherjee, KoushikBandyopadhyay, SoumikAngom, DilipMartin, Andrew M.Majumder, Sonjoyhttps://repository.iitgn.ac.in/handle/123456789/63062021-02-23T06:36:31Z2021-02-01T00:00:00ZDynamics of the creation of a rotating Bose Einstein condensation by two photon Raman transition using a Laguerre Gaussian laser pulse
Mukherjee, Koushik; Bandyopadhyay, Soumik; Angom, Dilip; Martin, Andrew M.; Majumder, Sonjoy
We present numerical simulations to unravel the dynamics associated with the creation of a vortex in a Bose–Einstein condensate (BEC), from another nonrotating BEC using two-photon Raman transition with Gaussian (G) and Laguerre–Gaussian (LG) laser pulses. In particular, we consider BEC of Rb atoms at their hyperfine ground states confined in a quasi two dimensional harmonic trap. Optical dipole potentials created by G and LG laser pulses modify the harmonic trap in such a way that density patterns of the condensates during the Raman transition process depend on the sign of the generated vortex. We investigate the role played by the Raman coupling parameter manifested through dimensionless peak Rabi frequency and intercomponent interaction on the dynamics during the population transfer process and on the final population of the rotating condensate. During the Raman transition process, the two BECs tend to have larger overlap with each other for stronger intercomponent interaction strength.
2021-02-01T00:00:00ZMagnetohydrodynamics model of an X-class flare in NOAA active region 12017 initiated with non-force-free extrapolationNayak, Sushree SangeetaBhattacharyya, RamitKumar, Sanjayhttps://repository.iitgn.ac.in/handle/123456789/63082021-02-23T07:41:35Z2021-02-01T00:00:00ZMagnetohydrodynamics model of an X-class flare in NOAA active region 12017 initiated with non-force-free extrapolation
Nayak, Sushree Sangeeta; Bhattacharyya, Ramit; Kumar, Sanjay
We present a three-dimensional magnetohydrodynamic simulation of the NOAA active region 12017 to explore the onset of an X-class flare on 2014 March 29 at 17:48 UT. The simulation is initiated with a magnetic field constructed by non-force-free-field extrapolation of the photospheric magnetic field. Importantly, the initial field contains a three-dimensional magnetic null, a pair of magnetic flux ropes, and a set of sheared arcades overlying the flux ropes at the flare location. A set of magnetic field lines are also identified which connect the flaring location to a distant region affected by the flare. The simulated evolution documents the magnetic reconnections at the null, which can potentially explain the observed chromospheric brightenings during the flare. The sheared arcades also appear to rise and participate in reconnections at the null. Notably, under the favorable initial Lorentz force, the flux ropes lose their twist due to reconnection. The terminal geometry of the ropes and the arcades are similar to the observed post-flare loops. Interestingly, the connecting field lines appear to take part in reconnections at the null, which may lead to the brightenings at the distant region. Further, the free energy released during the evolution which turns out to be ≈6.8×1031 ergs matches well with the observation.
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