Experimental Schematic: A transparent birefringent pattern of millimeter extension is imaged from 20 meters with two hyper-entangled photons.

This experiment was performed before we started quantum ghost imaging of a transparent pattern.  A transparent birefringent pattern of millimeter extension is quantum imaged directly (direct means a photon that has interacted with the pattern is detected by a camera, which is not the case in quantum ghost imaging). This experiment requires hyper-entangled photons consisting of momentum entanglement and polarization entanglement. The hyper-entanglement type in this experiment is different than a hyper-entanglement in a quantum ghost imaging experiment.

Publication: Quantum imaging of a polarization sensitive phase pattern with hyper-entangled photons. Manpreet Kaur, Mandip Singh, Sci.Rep. 11, 23636 (2021). PDF

This is a theory work that shows with a graphical proof that if one photon of an entangled pair is detected, then the second photon quantum state is determined immediately (EPR-argument), not only in the present but also in the past, when consistency is imposed in different relativistic inertial frames of references.

Publication: Nonlocal action at a distance also acts in the past. Mandip Singh. ArXiv: 2109.04151 (2021). PDF

This is a classic experiment with two double-slits, which is performed with momentum-entangled photons. In this experiment, photons are path entangled at slits thus, by detecting one photon. it is possible to find out through which slit the second photon has passed (which-slit information). If no such measurement is performed, then path entanglement leads to quantum interference of two photon measurements on two screens. Individual measurements of photon detection on each screen show no interference due to quantum entanglement. A path detection suppresses two photon quantum interference. 

Publication: Quantum double-double-slit experiment with momentum entangled photons, Manpreet Kaur and Mandip Singh, Sci.Rep. 10, 11427 (2020). PDF

In this experiment, a pattern is localized in a three-dimensional subspace of a six-dimensional phase space of atoms at room temperature, Figure-(a). This types of counter-intuitive patterns are completely delocalized in position space at a given time thus, cannot be imaged with lenses and cannot be comprehended directly.

The experiment is performed with Rubidium-87 atomic gas at room temperature by using velocity selective hole burning. The required phase space localized pattern is imprinted onto a phase space with laser beams of different frequencies. The tomographs of the phase space localized pattern are imaged by detuning another imaging laser beam with a resolution of 1 MHz. As a result, a three dimensional image of a pattern localized in a phase space, consisting of two spatial dimensions and one momentum dimension, is produced.

In this experiment, a transparent birefringent pattern is imprinted onto the phase space (in contrast to the previous experiment where an imprinted localized pattern was light absorbing). The pattern is localized in a 3D subspace of 6D phase space. The imprinted pattern is imaged by extracting subtomographs of a tomograph by varying the detuning of an imaging laser beam with a resolution of 100 KHz on the momentum axis. 

The experiment is performed in a phase space of Rubidium-87 atomic medium at room temperature by using atomic state dependent velocity selective hole burning.

Publication: Subtomographic imaging of a polarisation sensitive phase pattern localised in phase space. , Manpreet Kaur, Sheenam Saxena, Mandip Singh. Sci Rep. 14, 2641 (2024) . PDF

The Stern-Gerlach (SG) experiment is one of the most significant experiments in physics, which was performed to show the quantized nature of spin. Neutral atoms prepared in a state of nonzero spin, when passed through a strong magnetic field gradient, exhibit discrete trajectories. Classically, trajectories should be continuous, as a classical spin can be aligned at an arbitrary angle with the magnetic field.  However, in SG experiment, the magnetic field is classical, as it has a well-defined magnetic field at all points in space. 

In the quantum SG experiment (thought experiment),  the magnetic field is quantum superimposed, and spin is also quantized as it provides a complete quantum mechanical picture. Interesting physics arises as a special case if a spin polarized Bose-Einstein condensate (BEC) is passed through such a quantum magnetic field. The path of BEC is quantum entangled, which is equivalent to Schrodinger cat state.

Publication: Quantum Stern-Gerlach experiment and path entanglement of a Bose-Einstein condensate, Phys. Rev. A. 95, 043620, (2017). PDF

A flux qubit can be prepared in a quantum superimposed state of magnetic flux linked to it. In this paper, an external degree of freedom of rotation is introduced. The resulting Hamiltonian gives rich physics resulting in a natural coupling of angular displacement of a cantilever with magnetic flux linked to it when placed in a uniform magnetic field. The cantilever angular displacement and magnetic flux are quantum entangled in the ground state naturally, which is a Schrodinger cat state. A special case without Josephson junction is also investigated.

Publication: Macroscopic quantum oscillator based on a flux qubit. Mandip Singh, Phys. Letts. A. 379, 36, 2001-2006, (2015). PDF