Welcome to QPIA (Quantum Phenomena in Astrophysics) Lab
Probing quantum mechanical effects in astronomical media, mainly coherent phenomena, is one of my primary research interests, where I use theoretical quantum optics tools and numerical modelling to explain astronomical observations. I also love to study radio transients such as fast radio bursts and develop models to explain their observational characteristics. Along with my interests in astrophysics, I have developed theoretical quantum optics/quantum simulation toolboxes that are realizable in the laboratory.
Group members:
Postdoc: Mohammed Chamma (May 2023-present)
Research Associate: Vahid Anari (Oct 2023-present)
Graduate students: Ningyan Fang (July 2023, present, co-supervised with M. Houde), Toktam Rashidi (Sept, 2023), Ali Mohammdi (starting Sept 2024)
Undergraduate students: Victor Pop (Sept, 2023 -current), Subhradeep Mahata (Summer 2024), Zhejian Liu (May 2024-current)
Alumni: Arhum Siddiqui (Sept 2023-April2024)
Fast radio bursts (FRBs):
Fast radio bursts are short duration (~millisecond) bursts of energy at radio wavelengths exhibiting large brightness temperatures indicating that these signals originate from non-thermal objects through some coherent emission mechanism. The origin and underlying physical mechanism of FRBs remain unknown.
Modelling spectra of repeating fast radio bursts:
In a recent paper, my colleagues and I present a simple dynamical relativistic model that successfully explains phenomena previously observed in the dynamic spectra of FRBs (e.g., the temporal narrowing of bursts with increasing frequency and the downward frequency drift in a sequence of bursts with increasing arrival time (the so-called ``sad trombone'' effect)). Most interestingly, our model also predicts that a steeper frequency drift should be present within individual sub-bursts, with a drift rate scaling inversely with the sub-burst's temporal duration (henceforth the sub-burst drift law). This prediction was tested and verified in our paper using already published data from FRB~121102 collected over a wide range of frequencies. Moreover, in another newly submitted paper, we further investigate the sub-burst drift law using data available on two additional repeating FRBs, namely FRB~180814.J0422+73 and FRB~180916.J0158+65. We show that these two FRBs, along with FRB~121102, obey the same law (as shown in the figure below) despite residing in different types of galaxies located over a range of redshifts. For reasons discussed in those papers, these novel results provide strong evidence that the physical process responsible for the bursts of radiation in repeating FRBs may be universal and narrow-band in nature, while relativistic motions within the sources are required to explain the wide observed bandwidths.
Dicke's superradiance and fast radio bursts:
Dicke's superradiance, initially introduced in 1954 by Robert H. Dicke, is a cooperative behavior between interacting atoms or molecules. When certain conditions are met, the group of excited atoms/molecules act as a unit and radiation rates are significantly enhanced. This results in a strong directional radiation beam over a shorter time-scale. Astronomers tend to ignore coherent effects such as superradiance and consider the ISM as a mostly non-coherent medium. In our papers [1, 2], we show that superradiance models can provide a simple explanation for FRBs and elegantly reproduce several of their observed characteristics.
Dicke's superradiance and maser flares:
Astronomical masers (microwave amplification by stimulated emission of radiation) are intense radiation bursts found in circumstellar envelope of evolved stars, star-forming regions, central parsecs of AGNs, etc. There are so far an upward of nine molecules known to exhibit masing behavior in astronomical media. Masers require population inversion and velocity coherence along the line-of-sight. The inversion can be acheived through a radiative pump.
Some radiation flares detected in maser hosting regions are found to exhibit fast flux rise times and asymmetric light curves that are not consistent with changes in their pump and cannot be simply explained within the context of maser theory. To explain these observations, we use Dicke's superradiance model. We show an increase in the pump rate and the inverted population density of only a factor of a few results in a significant increase in radiation. While the changes in the pump rate can take place over a few hundred days, the rise in radiation flux density when superradiance is initiated is drastic and happens over a much shorter time-scale.
So far, we have developed superradiance models to explain some maser flares detected at the 6.7-GHz methanol, 1612-MHz OH, and 22-GHz water spectral lines.
On the left, I show the superradiance models for flaring events at the 6.7 GHz methanol line detected in three different star-forming regions (G24.329, Cepheus A, and S255IR-NIR3). Please see our paper for more details.
Superradiance and masers; two complementary effects
In a recent paper published in MNRAS, we provide a unifying picture where we show Dicke's superradiance and astronomical masers are not competing phenomena but are rather complementary and define two distinct limits for the intensity of radiation. Masers characterize the quasi-steady state limit, when the population inversion density and the polarization amplitude vary on time-scales longer than those of non-coherent processes affecting their evolution (e.g. collisions), while superradiance defines the fast transient regime taking place when these conditions are reversed. We show how a transition from a maser regime to superradiance will take place whenever a critical threshold for the column density of the population inversion is reached, at which point a strong level of coherence is established in the system and a powerful burst of radiation can ensue during the transient regime. This critical level also determines the spatial region where a transition from the unsaturated to the saturated maser regimes will take place; superradiance can thus be seen as the intermediary between the two.
Quantum simulation with trapped ions:
Engineering higher dimensional lattices allows potentially the ability to probe a rich variety of physical phenomena, such as quantum transport and localization. Trapped ions are among the most versatile platforms for quantum simulation, especially for simulating quantum spin systems owing to their inherent long-range interactions even when the ions are situated in a 1D topology. We propose a hybrid method of analog digital quantum simulation where we dynamically modify a fully-connected 1D ion chain to, engineer in an arbitrary 2D lattices. In this method the required control parameters scale linearly with ion number. This hybrid approach offers compelling possibilities for the use of 1D chains in the study of Hamiltonian quenches, dynamical phase transitions, and quantum transport in 2D and 3D. The results of our work is published in a paper in NPJ QI.