arXiv subjects

Diptaranjan Das

Publications and source records attributed to Diptaranjan Das.

5 recordsLinked to original sources

arXiv2026

Stability of a high-finesse optical cavity at 493 nm in vacuum for cavity QED with Barium ions

We explore the stability of a high-finesse optical cavity at 493 nm in vacuum for cavity QED with Barium ions. A high-finesse Fabry-Perot cavity is built using mirrors with high-reflectivity (HR) coatings that are implemented by stacking multiple thin films of low-loss dielectrics on substrates. Applications of such HR mirrors in the near ultraviolet (UV) range have been hampered by degradation of coatings in vacuum. Here, we explore the degradation of mirrors with HR coatings at 493 nm in vacuum. We study both vacuum-induced and laser-induced effects on oxide-coated cavity mirrors by probing changes in cavity loss using cavity lifetime measurements. We investigate the role of circulating power in the rate of increase in cavity loss and demonstrate methods of reversal of cavity degradation. While we observe no degradation without long exposure or with short exposures at lower circulating powers, we find evidence of degradation on long exposure to high circulating powers. We discuss potential causes and conclude that laser-induced deposition is the likely cause while ruling out thermally activated processes due to laser-induced heating.

physics.optics↗

arXiv2020

Subradiance and superradiance-to-subradiance transition in dilute atomic clouds

We experimentally study subradiance in a dilute cloud of ultracold rubidium (Rb) atoms where $n λ_a^3 \approx 10^{-2}$ ($n$: atomic density, $λ_a$ excitation wavelength) and the on-resonance optical depth of the cloud is of order unity. We show that in the strong excitation regime, the subradiant time-scales depend on the excitation fraction of the cloud; i.e., to the intensity of the excitation pulse. In this regime, the decay dynamics are highly complicated and there is not a single decay time-constant. Instead, the decay time constant varies during the dynamics. Specifically, we were able to observe signatures of superradiant-to-subradiant transition; i. e., initially the decay rate is faster than independent decay (superradiant emission), while at later times it transitions to slower (subradiant emission). We also discuss a theoretical model whose numerical results are in good agreement with the experiments.

quant-ph↗

arXiv2012

Quantification of Entanglement from Magnetic Susceptibility for a Heisenberg Spin 1/2 system

Temperature and magnetic field dependent magnetization and extraction of entanglement from the experimental data is reported for dichloro(thiazole)copper(II), a Heisenberg spin chain system. The magnetic susceptibility vs. temperature plot exhibits signature of infinite spin chain. Isothermal magnetization measurements (as a function of magnetic field) were performed at various temperatures below the antiferromagnetic (AFM) ordering, where the AFM correlations persist significantly. These magnetization curves are fitted to the theoretically generated Bonner-Fisher model. Magnetic susceptibility can be used as a macroscopic witness of entanglement; using which entanglement is extracted from the experimentally measured magnetic data.

cond-mat.str-el↗

arXiv2012

Comparative Study of Magnetic Behaviour in Three Classic Molecular Magnets

We have studied the magnetic properties of three phenalenyl based organic neutral radicals. The first one is a Heisenberg chain antiferromagnet with one unpaired spin per molecule; second one is a diamagnetic, exhibiting a diamagnetic to paramagnetic phase transition at high temperature; the third one comprises of free neutral radicals and shows paramagnetic behaviour. Temperature dependent magnetic susceptibility measurements and isothermal magnetization measurements (as a function of magnetic field) were performed on all the three systems. In the case of the antiferromagnetic system, temperature dependent susceptibility and magnetization isotherms were fitted to the Bonner Fisher model. In the case of second system the diamagnetic to paramagnetic phase transition is investigated by performing isothermal magnetization measurements in the two different phases. The diamagnetic to paramagnetic phase transition seems to be of first order in nature.

cond-mat.str-el↗

arXiv2011

Experimental detection of quantum information sharing and their quantification in quantum spin systems

We study the macroscopic entanglement properties of a low dimensional quantum spin system by investigating its magnetic properties at low temperatures and high magnetic fields. The tempera- ture and magnetic field dependence of entanglement from the susceptibility and magnetization data comparing the experimental extraction with theoretical estimates are given. Extraction of entan- glement has been made possible through the macroscopic witness operators magnetic susceptibility. The protocol followed in doing so has been outlined in some recent work. Various plots of entan- glement comparing the experimental extraction with theoretical estimates are given. Quantitative comparison between concurrence and entanglement witness is given for both the theoretical and experimental results. Theory and experiments match over a wide range of temperature and field. The spin system studied is a chain, which exhibits dimerisation and yields fascinating entanglement properties when the temperature and magnetic field is varied. These spin systems exhibit quantum phase transition (QPT) at low temperatures, when the magnetic field is swept through a critical value. We show explicitly for the first time, using tools used in quantum information processing (QIP), that quantum phase transition (QPT) can be captured experimentally using canonically conjugate observables. Macroscopically, quantum complementarity relation clearly delineates entangled states from separable states across the QPT. We have estimated the partial information sharing in this system from our magnetization and susceptibility data. The complementarity relation has been experimentally verified to hold in this system

quant-ph↗