Anis Rahman

My research is focused on using spins such as those of nitrogen-vacancy centres in diamonds to develop new quantum sensors, e.g., magnetic field sensors, with the aim of measuring signals from human hearts and brains, detecting hidden objects such as sewage/gas lines as well as performing geological surveys, and magnetic navigation. My research sits within the broader Warwick QuantumLink opens in a new window initiatives.

Grants

A. T. M. Anishur Rahman (PI), "NV centres in diamond-based Faraday magnetometer," Warwick Innovations, £59,729, 2024-2025.
A. T. M. Anishur Rahman (PI) and G. Morley (Co-I), "A new ultra-sensitive NV centre in diamond based magnetometer," EPSRC IAA 2022-25, £66,989, 2023-2024.
G. Morley (PI) and A. T. M. Anishur Rahman (Co-I), "Magnetic flux concentrators to increase the sensitivity of diamond magnetometers for medical diagnosis," EPSRC IAA 2022-2025, £19,713, 2022.
P. F. Barker (PI), A. T. M. Anishur Rahman (Co-I) and S. Bose (Co-I), "Laser refrigeration on the nanoscale: From nanocryostats to quantum optomechanics," EPSRC (EP/S000267/1), £729,667, 2018-2022.

Patents

A T M Anishur Rahman, "NVito: A solid-state atomic magnetometer," GB2312664, August 2023.

Publications

Preprints

For my other publications see my Google Scholar page

Reviewer

I review URKI Grants. I am also review journals in my field including New Journal of Physics, Physical Review X, Nature Communications and others.

Student supervision

I currently supervise three PhD students as a second supervisor.

Karishma Gokani
Stuart Graham
Alex Newman

Research Interests

Magnetometry

NV centres in diamond

Faraday Magnetometer

We have developed a new magnetic field sensor (magnetometer)Link opens in a new window using NV centres in diamonds and the Faraday effect . The sensitivity of this magnetometer is 300 nanotesla - meaning that it can detect fields 100 times weaker than the earth's magnetic field. The sensitivity of the new magnetometer can reach femtotesla with some modification/improvement to the existing experiment.

In a Faraday magnetometer a pump laser beam excites the sensors, here NVCs, to their magnetically sensitive states and a linearly polarized probe laser beam measures the states of the sensors. As the probe beam interacts with NVCs, its plane of polarization gets rotated. This rotation can be measured using a standard polarizing beam splitter and a photodetector. Magnetic fields to be measured perturb the sensor and this is reflected in the photodetector signal. With an appropriate calibration, the direction and amplitude of the unknown magnetic field can be determined from the photodetector signal. In the current version of the Faraday magnetometer, a single laser beam is used as a pump and a probe. Separate probe beams provide better sensitivities .

A team is now working on improving the performance of this new magnetometer using optical cavities and other quantum tricks. Previously, a PDRA was working on this project.

Levitated magnetic particles as ac magnetic field sensors

Electromagnetic waves are widely used including in defense, biomedicine, and fundamental science. Their efficient detection determines how we communicate, defend against adversaries, diagnose diseases and perform search and rescue operations. In this article, exploiting the precession of a levitated magnetic particle in ultra-high vacuum, we show that weak electromagnetic waves down to the femtotesla level can be detected. It is also shown that such a sensor has a large dynamic range over a millitesla, is continuously tunable over many gigahertz and can detect frequencies with sub-hertz resolutions. The direction of arrival of the incoming electromagnetic wave can also be found relatively easily.

For further details see ( Archive HAL for an earlier versionLink opens in a new window).

Ferromagnet based Faraday magnetometer for dark matter search

Our universe consists of 5% normal matter which includes all the objects that we can see e.g. planets, stars, galaxies etc, 27% dark matter (does not interact with light hence dark) and 68% dark energy. Dark energy is believed to be responsible for the expansion of our universe while dark matter is considered to be behind the large scale astronomical structures e.g. galaxies. Dark matter can be hot, warm and cold. As per our current understanding hot dark matter is not detectable. Axion, a hypothetical particle, is considered to be one of the main constituents of cold dark matter. Its mass is predicted to between 10^-7 μeV and 10⁴ μeV. I have recently proposed a scheme which can search axions between 500 μeV and 5000 μeV. In this scheme, I use a magnetic rod placed inside a high finesse optical cavity and the Faraday effect. The optical cavity can be formed by using two mirrors or by coating the ends of the magnets with appropriate mirror coatings. A probe laser propagates through the long axis of the magnetic rod while the magnetization of the magnet is in the perpendicular direction of the light field propagation direction. More details can be found in the paper titled "Ultrawideband axion search using a Faraday haloscope"Link opens in a new window.

Other research interests

The superposition principle is one of the fundamental tenets of quantum mechanics. According to it, an object can be in multiple states at the same time. For example, it can be up and down at the same time. While this is weird, over the years many experiments have confirmed this. The heaviest object so far put into such a state weighs about 10^-23 kgLink opens in a new window. In the past, I have worked in projects with the aim of putting a nanodiamond containing a single NVC into a spatial superpositionLink opens in a new window e.g. left and right at the same time.

In a recent article, I have proposed a theoretical scheme which can create a large spatial superposition. In this proposed scheme, I use a levitated magnetic particle which contains many coherently coupled spins. In a small nanomagnet, all spins are strongly coupled with each other via the exchange coupling and they behave as a single entity. The magnetic moment (m) of such a tiny magnet can switch between north and south. At high temperature this is called superparamagnetism while at low temperature (< 1 K) where the thermal fluctuations are not viable (not enough thermal energy left), quantum fluctuations (roughly speaking) appear. This quantum fluctuation is known as tunneling. From quantum mechanics we know that when tunneling is allowed,a superposition of the states emerges. In this case, a superposition of the north and the south pole $(\vert N\rangle+\vert S\rangle)/\sqrt{2}$. In the scheme that I have proposed, I use this north- south spin superposition in combination with a magnetic field gradient for the creation of a spatial superposition or a Schrodinger cat. For a 20 nm magnetic particle, the spatial superposition can be up to 2 micrometers- significantly larger than the object itself. More details can be found in the article titled "Large spatial Schrödinger cat state using a levitated ferrimagnetic nanoparticleLink opens in a new window"

Departmental Responsibility

I sits in PDRA shortlisting and interview panels as well as PhD students recruitment panels.

Warwick Open Day

I help colleagues who organize the University of Warwick Open Days. As a part of this activity, I demonstrate different experiments to the perspective students and their parents. Below are some photographs which were taken when I was demonstrating our photon entanglement experiments to the visitors.

Outreach

Research Culture

I have recently participated in a research culture projectLink opens in a new window and it was real fun.

School talks

To raise awareness quantum technologies and science and thus the potential benefit of studying STEM subjects, I give talks at local high schools in Coventry. In this talk, I give a very general overview of the fundamental laws of physics - in particular quantum mechanics. I also highlight the counter-intuitive nature of quantum mechanical laws e.g., entanglement and superpositions and their potential usage in developing new technologies. I also show different experiments that I am currently doing at Warwick. Some photographs from these talks are shown below

Sydney Stringer Academy, Hillfield, Coventry

Sydney Stringer Academy, Hillfields, Coventry Stringer3

Finham Park School, Finham, Coventry

Article in ScienceX Dialog

I wrote a news article on spatial superpositions Link opens in a new windowfor ScienceX Dialog run by Phys.Org. This is based on my theoretical article on how to create large spatial superpositionsLink opens in a new window or Schrodinger cats using spin tunneling magnetic particles. In this article, I portray the idea of spatial superposition by showing a child lives in New York and London at the same time (see photograph below).

Spatial Superposition