Joyee Ghosh - Academia.edu (original) (raw)

Papers by Joyee Ghosh

In this paper, we study the possible parametric down-conversion processes in a type II phase-matc... more In this paper, we study the possible parametric down-conversion processes in a type II phase-matched, Lithium Niobate ridge waveguide, designed to generate photon pairs in the telecommunication range. A quantum analysis of spontaneous parametric down-conversion (SPDC), first, with a pulsed Gaussian pump beam and second, with a pulsed, spatially anti-symmetric Hermite-Gaussian HG (1,0) pump beam predict the possible down conversion processes in each case. In case of the former, degenerate photon pairs are emitted at 1550 nm with the highest efficiency in the fundamental waveguide mode. While, in case of the latter, non-degenerate photon pairs in different higher-order spatial modes are generated. The joint spectral amplitude (JSA) analysis of these processes, prove that the generated photons pairs having orthogonal polarizations are negatively correlated. With multiple degrees of freedom, like polarization and spatial modes, such photons can be further harnessed towards modal-entangl...

The absorption of one photon of an entangled pair by a lone trapped atom is identified by a corre... more The absorption of one photon of an entangled pair by a lone trapped atom is identified by a correlation between the atomic absorption process and the detection of the second photon.

Journal of Optics

We study modal characteristics of a customized ridge waveguide in Lithium Niobate designed to gen... more We study modal characteristics of a customized ridge waveguide in Lithium Niobate designed to generate twin photons at telecom wavelength. A quantum analysis of SPDC predicts the possible down conversion processes and optimizes the input beam parameters for fundamental mode emission. Further, a Joint Spectral Amplitude (JSA) analysis ensures the generation of signal/idler photons at 1550 nm in the customized LN waveguide. A calculation of the parametric down conversion (PDC) signal power shows a dependence of ℒ 3 2 ⁄ for a waveguide compared to a linear dependence in case of a bulk crystal.

Journal of Optics, Jun 13, 2018

Physical Review A

In this paper, we propose a single integrated waveguide device to generate two different polariza... more In this paper, we propose a single integrated waveguide device to generate two different polarization-entangled Bell states involving nondegenerate photon pairs (with the signal photons being emitted in the telecom C band) by utilizing type-0, type-I, and type-II quasi-phase-matching (QPM). In this context, we have studied ppKTP (periodically-poled potassium titanyl phosphate) in detail. To obtain polarization entanglement of the emitted photons, we have used two different situations, two cascaded QPM gratings (of the same length) to obtain |ψ + , and two separate QPM gratings (of different lengths) to obtain |φ +. In such a scenario, maximal entanglement can be quantified in terms of overlap bandwidths of the two phase-matched processes.

13th International Conference on Fiber Optics and Photonics, 2016

Quantum Communications and Quantum Imaging XIII, 2015

A three-level atom in a Lambda\LambdaLambda configuration trapped in an optical cavity forms a basic unit i... more A three-level atom in a Lambda\LambdaLambda configuration trapped in an optical cavity forms a basic unit in a number of proposed protocols for quantum information processing. Through control with an appropriate laser, this system allows for efficient storage of cavity photons into long-lived atomic excitations, and their retrieval with high fidelity. This process presumes an adiabatic transfer through the `dark state', a coherent superposition of the two lower levels of the Lambda\LambdaLambda system, by a slow variation of the intensity of the control laser. We study the full quantum mechanics of this transfer process with a view to examine the nonadiabatic effects, as the control laser is varied in time. The nonadiabatic effects arise due to inevitable excitations of the system to states involving the highest level of the Lambda\LambdaLambda configuration, which is radiative. We formulate the problem in terms of the instantaneous eigenstates and solve it numerically, allowing for spontaneous decays from t...

Laser Physics

Electromagnetically-induced transparency (EIT) in three-level Λ-systems is based on quantum inter... more Electromagnetically-induced transparency (EIT) in three-level Λ-systems is based on quantum interference effects involving coherence between the two lower levels, which allow propagation of a resonant probe light beam in the presence of a strong coupling field. We have observed transparency in ultra-narrow (<10 kHz) windows at the resonant 1.083 μm transition for purely electronic spins in gaseous 4He* at room temperature. Slow light is an interesting outcome of the EIT phenomenon due to extreme dispersion within the narrow transparency window. We have obtained group delays of about 4 μs in a 2.5 cm long He* cell. A complete theoretical analysis explains our observations emphasizing the positive role of collisions. Slow light with 1GHz Doppler broadening opens the door to applications of controllable large-bandwidth delays in radars.

Nature Physics

Emission and absorption of single photons by single atoms is a fundamental limit of matter–light ... more Emission and absorption of single photons by single atoms is a fundamental limit of matter–light interaction, manifesting its quantum mechanical nature. As a controlled process, it is also a key tool in quantum optical information technology 1, 2, 3. Controlled single-photon emission is well advanced 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14; for controlled single-photon absorption by a single atom, proposals exist but only preliminary experimental steps have been taken 15, 16, 17, 18, 19. Here we report the absorption of single photons by a single trapped ion: employing a photon pair source, detection of the quantum-correlated partner photon heralds the presence of the resonant photon at the atom. We find clear correlations between the detection of the herald and the absorption process in the atom; we also demonstrate polarization control of this process. Our experiment evidences previously unexplored interaction between a single absorber and a quantum light source; with improved contro...

We demonstrate single trapped ion-single heralded photon interaction by the detection of quantum ... more We demonstrate single trapped ion-single heralded photon interaction by the detection of quantum jumps, strongly correlated with the detection of the heralding photon. This is a step towards controlling single-photon absorption and photon-to-atom entanglement transfer.

Advances in Slow and Fast Light II, 2009

In a Λ-type atomic system with electromagnetically-induced transparency, we probe the fidelity of... more In a Λ-type atomic system with electromagnetically-induced transparency, we probe the fidelity of the storage and retrieval of an electromagnetic signal, as the control laser field is varied with time. We study numerically the adiabatic transfer problem for an isolated atom, and show that for a weak signal, even the slowest variations of the control field take the system out of the dark state, which is a coherent superposition of the two lower levels of the Λ system. Following this, we incorporate the effect of dissipation on system dynamics by allowing for spontaneous decay of the system to the lower levels in a wavefunction approach. We conclude that dissipation definitely aids the retrieval process but not so much the storage. Further, for storing the signal, the control field should be switched off as slowly as possible, but while retrieving it, the faster we switch on the control field, the better the signal is retrieved. Also, for a given system there is an optimal control power for the best retrieval. Our results find partial support in the reported experimental observations.

2011 Conference on Lasers and Electro-Optics Europe and 12th European Quantum Electronics Conference (CLEO EUROPE/EQEC), 2011

We study the controlled interaction between a single trapped 40 Ca + ion and single photons belon... more We study the controlled interaction between a single trapped 40 Ca + ion and single photons belonging to entangled photon pairs. The ion is prepared as a polarization-sensitive single-photon absorber; the absorption of one photon from a pair is marked by a quantum jump of the atomic state and heralded by the coincident detection of the entangled partner photon. For three polarization basis settings of absorption and detection of the herald, we find maximum coincidences always for orthogonal polarizations. Tomographic reconstruction of the biphoton quantum state from the absorption-herald coincidences reveals 93% overlap with the maximally entangled state. This proves that the polarization entanglement shared by the photon pair is preserved in the absorption process and converted to transient photon-atom entanglement.

Physical Review A, 2007

We quantitatively analyze the dynamics of the quantum phase distribution associated with the redu... more We quantitatively analyze the dynamics of the quantum phase distribution associated with the reduced density matrix of a system, as the system evolves under the influence of its environment with an energy-preserving quantum nondemolition (QND) type of coupling. We take the system to be either an oscillator (harmonic or anharmonic) or a two-level atom (or equivalently, a spin-1/2 system), and model the environment as a bath of harmonic oscillators, initially in a general squeezed thermal state. The impact of the different environmental parameters is explicitly brought out as the system starts out in various initial states. The results are applicable to a variety of physical systems now studied experimentally with QND measurements.

Conference on Lasers and Electro-Optics 2010, 2010

We demonstrate single trapped ion-single photon interaction by the detection of quantum jumps, st... more We demonstrate single trapped ion-single photon interaction by the detection of quantum jumps, strongly correlated with the detection of the quantum-correlated heralding photon. This is a step towards controlling single-photon absorption and transferring photon-to-atom entanglement.

Physical Review A, 2009

We present a realistic theoretical treatment of a three-level Λ system in a hot atomic vapor inte... more We present a realistic theoretical treatment of a three-level Λ system in a hot atomic vapor interacting with a coupling and a probe field of arbitrary strengths, leading to electromagneticallyinduced transparency and slow light under the two-photon resonance condition. We take into account all the relevant decoherence processes including collisions. Velocity-changing collisions (VCCs) are modeled in the strong collision limit effectively, which helps in achieving optical pumping by the coupling beam across the entire Doppler profile. The steady-state expressions for the atomic density-matrix elements are numerically evaluated to yield the experimentally measured response characteristics. The predictions, taking into account a dynamic rate of influx of atoms in the two lower levels of the Λ, are in excellent agreement with the reported experimental results for 4 He*. The role played by the VCC parameter is seen to be distinct from that by the transit time or Raman coherence decay rate.

New Journal of Physics, 2013

We use a single trapped 40 Ca + ion as a resonant, polarizationsensitive absorber to detect and c... more We use a single trapped 40 Ca + ion as a resonant, polarizationsensitive absorber to detect and characterize the entanglement of tunable narrowband photon pairs from a spontaneous parametric down-conversion source. Single-photon absorption is marked by a quantum jump in the ion and heralded by coincident detection of the partner photon. For three polarization basis settings of the absorption and detection of the herald, we find maximum coincidences always for orthogonal polarizations. The polarization entanglement is further evidenced by tomographic reconstruction of the biphoton quantum state with an overlap fidelity of 93% with the Bell singlet state. This is an essential step toward a single-ion based quantum memory for photonic entanglement. Content from this work may be used under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Nature Physics, 2011

The emission and absorption of single photons by single atomic particles is a fundamental limit o... more The emission and absorption of single photons by single atomic particles is a fundamental limit of matter-light interaction, manifesting its quantum mechanical nature. At the same time, as a controlled process it is a key enabling tool for quantum technologies, such as quantum optical information technology [1, 2] and quantum metrology [3, 4, 5, 6]. Controlling both emission and absorption will allow implementing quantum networking scenarios [1, 7, 8, 9], where photonic communication of quantum information is interfaced with its local processing in atoms. In studies of single-photon emission, recent progress includes control of the shape, bandwidth, frequency, and polarization of single-photon sources [10, 11, 12, 13, 14, 15, 16, 17], and the demonstration of atom-photon entanglement [18, 19, 20]. Controlled absorption of a single photon by a single atom is much less investigated; proposals exist but only very preliminary steps have been taken experimentally such as detecting the attenuation and phase shift of a weak laser beam by a single atom [21, 22], and designing an optical system that covers a large fraction of the full solid angle [23, 24, 25]. Here we report the interaction of single heralded photons with a single trapped atom. We find strong correlations of the detection of a heralding photon with a change in the quantum state of the atom marking absorption of the quantum-correlated heralded photon. In coupling a single absorber with a quantum light source, our experiment demonstrates previously unexplored matter-light interaction, while opening up new avenues towards photon-atom entanglement conversion in quantum technology.