arXiv subjects

Selim M. Shahriar

Publications and source records attributed to Selim M. Shahriar.

At least 19 recordsLinked to original sources

arXiv2026

Slow Light Augmented Unbalanced Interferometry for Extreme Enhancement in Sensitivity of Measuring Frequency Shift in a Laser

We demonstrate a slow-light augmented unbalanced Mach-Zehnder interferometer (MZI) which can be used to enhance very significantly the sensitivity of measuring the frequency shift in a laser. The factor of enhancement depends on the group index of the slow-light medium, the degree of imbalance between the physical lengths of the two arms of the MZI, and the spectral width of the laser. For a laser with a quantum noise limited spectral width, the group index has to be larger than the finesse of the laser cavity in order to achieve enhancement in measurement sensitivity. For the reported results, slow-light effect is produced by employing electro-magnetically induced transparency via coherent population trapping in a paraffin coated vapor cell of Rb atoms, with a maximum group index of ~2170. The maximum enhancement factor realized is ~70. This differs from the theoretically expected value of ~183 by a factor of ~2.6. This discrepancy can be attributed to effects of unidentified excess noise, and the fact that the test laser spectral width may not the quantum noise limited. Much larger values can potentially be obtained by modifying the apparatus, and using cold atoms for producing the slow-light effect. The sensitivity of any sensor that relies on measuring the frequency shift of a laser can be enhanced substantially using this technique. These include, but are not limited to, gyroscopes and accelerometers based on a conventional ring laser or a superluminal ring laser, and detectors for virialized ultra-light field dark matter.

quant-ph↗

arXiv2026

Slow Light Augmented Fabry-Perot Cavity for Enhanced Sensitivity in Measuring Frequency Shift

Recently, it has been shown that a slow-light augmented unbalanced Mach-Zehnder interferometer (SLAUMZI) can be used to enhance significantly the sensitivity of measuring the frequency shift of a laser, compared to the heterodyne technique. Here, we show that a similar enhancement can be realized using a slow-light augmented Fabry-Perot Cavity (SLAFPC), due to the fact that an FPC is inherently unbalanced, since different bounces of the field traverse different path lengths before interfering with the other bounces. We show how the degree of enhancement in sensitivity depends on the spectral width of the laser and the finesse of the FPC. For potentially realizable conditions, we show that a sensitivity enhancement factor ~2.8*10^6 can be achieved using a SLAFPC.

physics.optics↗

arXiv2026

The General Quantum Limit for and the Optimization of the Minimum Measurable Frequency Shift in a Laser

We show that, contrary to conventional understanding, the minimum measurable frequency shift (MMFS) for a single-mode ideal laser is determined by a combination of phase diffusion caused by SE and the shot noise caused by the VM. For all practical sensors, the MMFS is found to be given by the geometric mean of the measurement bandwidth and the Schwalow-Townes Linewidth, multiplied by a factor which can be much larger than unity under certain conditions. We determine the optimal value for the MMFS for three different sensing modalities, an unbalanced Mach-Zehnder Interferometer, a passive Fabry-Perot cavity (FPC), and heterodyning with a reference laser, and identify the conditions needed for reaching the optimal value.

quant-ph↗

arXiv2026

Optical injection locking of white light cavity based superluminal lasers

Optical injection locking is a simple method for synchronizing a laser to an external laser source by injecting part of the external laser light into the cavity of the other laser. This approach received significant interest due to its potential applications in telecommunications, precision metrology, and more. We study and analyze the steady-state and dynamic properties of optical injection locking in white light cavity (WLC) lasers. We derive the steady-state injection locking range of the WLC laser and the dynamic (Adler) equation for the phase-difference between the injected signal and the locked laser output. The analysis shows that WLC lasers can exhibit an order of magnitude broader locking range and three order of magnitudes faster dynamics compared to conventional lasers with similar thresholds and free spectral ranges.

physics.optics↗

arXiv2026

Impact of spontaneous emission on spin-squeezed quantum sensors

The echo squeezing protocols (ESPs) are techniques that amplify the phase shift in a quantum sensor with one-axis-twist squeezing (OATS). For atomic sensors, spontaneous emission (SE) in the OATS operations is an important imperfection, which, however, is prohibitively difficult to study. SE can transfer atoms to all the Zeeman substates, making the number of relevant collective states excessively large. In this paper, we focus on a relatively simple isotope, namely Sr-88, which only has one Zeeman substate in each of the two ground states. Nevertheless, studying the effect of SE is still challenging because SE will populate all collective states, either symmetric or asymmetric, thus putting the ensemble into a mixed state. Based on analytical derivation and numerical simulations, we conclude that the GESP is more resistant to SE than the conventional echo squeezing protocol (CESP). This is another advantage of the GESP that has not been realized formerly. We also find that for the GESP employing Sr-88, the SE-induced reduction in the signal contrast is the same as that for a Ramsey protocol without squeezing and the quantum noise is suppressed by SE. This is an unexpectedly favorable result. The SE-induced suppression of quantum noise constitutes a previously unrecognized effect that challenges both earlier conclusions and intuitive expectations.

quant-ph↗

arXiv2026

Modified One-Axis-Twist Squeezing for Deterministic Orientation Control of Schrödinger Cat States with Unknown Atom-Number Parity

The Schrödinger cat state protocol (SCSP) makes use of a Schrödinger cat (SC) state generated with one-axis-twist squeezing (OATS) to enhance the sensitivity. In principle, the SCSP can magnify the phase shift by a factor N, the number of atoms under interrogation, accompanied by a quantum noise amplification by a factor of root-N, enabling an atomic sensor to reach the Heisenberg limit. However, the current SCSP can reach this benchmark only if the parity of N is known, which is almost impossible for a large ensemble. The reason is the orientation of the SC state generated with the conventional OATS depends on the parity of N. In this paper, we propose a modified OATS (MOATS) operation that generates the SC state aligned in a certain direction regardless of the parity of N.

quant-ph↗

arXiv2026

Opto-Atomic Spatio-Temporal Holographic Correlators for High-Speed 3D CNNs

Three-dimensional convolutional neural networks (3D CNNs) have demonstrated remarkable performance in video recognition tasks by processing both spatial and temporal features. However, the cubic scaling of computational complexity poses significant time and energy efficiency challenges for conventional silicon-based hardware. To address this, we propose a hybrid optoelectronic architecture that delegates the computationally intensive 3D convolutional layer to an opto-atomic Spatio-temporal Holographic Correlator (STHC). This system stores temporal information as atomic coherence in an array of inhomogeneously broadened cold Rubidium-85 atoms and combines a traditional 2D spatial correlator to perform correlation in both space and time simultaneously. Our results on a four-class human action dataset demonstrate a classification accuracy of 59.72% using parallel large-scale kernels (30X40 pixels spatially, 8 frames temporally), with potential operating speeds projected up to 125,000 frames per second. This approach offers a pathway to massively accelerated video classification through a hybrid architecture.

cs.AR↗

arXiv2025

Debiased Opto-electronic Joint Transform Correlator for Enhanced Real-Time Pattern Recognition

Opto-electronic joint transform correlators (OJTCs) use a focal plane array (FPA) to detect the joint power spectrum (JPS) of two input images, projecting it onto a spatial light modulator (SLM) to be optically Fourier transformed. The JPS is composed of two self-intensities and two conjugate-products, where only the latter produce the cross-correlation. However, the self-intensity terms are typically much stronger than the conjugate-products, producing a bias that consumes most of the available bit-depth on the FPA and SLM. Here we propose and demonstrate, through simulation and experiment, a debiased OJTC (DOJTC) that electronically pre-processes the JPS to remove the self-intensity terms before sending it to the SLM, thereby enhancing the quality of the cross-correlation result. We show that under some conditions the DOJTC yields a nearly two orders of magnitude improvement in the signal-to-noise ratio compared to an OJTC.

eess.IV↗

arXiv2025

Automatic Event Recognition Employing Optically Excited Electro-Nuclear Spin Coherence

An analog automatic event recognition (AER) system can be realized by combining the technique of holographic image recognition with the process of temporal signal correlation employing stimulated photon echo in an ensemble of two-level atoms. For efficient operation of the AER system, the optical transition in the two-level system must have a large oscillator strength. However, this implies a rapid decay of the excited state, which highly constrains the duration of the event that can be recognized, even when the images are retrieved rapidly from a fast parallel optical memory device. This constraint can be overcome by using a three-level Lambda system to transfer optical coherence to long-lived electro-nuclear spin coherence and vice-versa. Here, we present an analysis of the AER process employing such a Lambda system. We also show that due to the longitudinal and transverse variation of the phases of the optical fields undergoing Fresnel diffraction, the density matrix equations must account for the differences in the phases of the coherence excited in each pixel and the corresponding phases of the optical fields in subsequent pulses.

quant-ph↗

arXiv2025

Shift, Scale and Rotation Invariant Multiple Object Detection using Balanced Joint Transform Correlator

The Polar Mellin Transform (PMT) is a well-known technique that converts images into shift, scale and rotation invariant signatures for object detection using opto-electronic correlators. However, this technique cannot be properly applied when there are multiple targets in a single input. Here, we propose a Segmented PMT (SPMT) that extends this methodology for cases where multiple objects are present within the same frame. Simulations show that this SPMT can be integrated into an opto-electronic joint transform correlator to create a correlation system capable of detecting multiple objects simultaneously, presenting robust detection capabilities across various transformation conditions, with remarkable discrimination between matching and non-matching targets.

eess.IV↗

arXiv2025

Temporal Scale and Shift Invariant Automatic Event Recognition using the Mellin Transform

The Spatio-temporal holographic correlator combines the traditional 2D optical image correlation techniques with inhomogeneously broadened arrays of cold atoms to achieve 3D time-space correlation to realize automatic event recognition at an ultra-high speed. Here we propose a method to realize such event recognition for videos running at different speeds. With this method, we can highly improve recognition accuracy and filter almost all the unwanted events in the video database.

cs.CV↗

arXiv2025

Ultra-fast Real-time Target Recognition Using a Shift, Scale, and Rotation Invariant Hybrid Opto-electronic Joint Transform Correlator

Hybrid Opto-electronic correlators (HOC) overcome many limitations of all-optical correlators (AOC) while maintaining high-speed operation. However, neither the OEC nor the AOC in their conventional configurations can detect targets that have been rotated or scaled relative to a reference. This can be addressed by using a polar Mellin transform (PMT) pre-processing step to convert input images into signatures that contain most of the relevant information, albeit represented in a shift, scale, and rotation invariant (SSRI) manner. The PMT requires the use of optics to perform the Fourier transform and electronics for a log-polar remapping step. Recently, we demonstrated a pipelined architecture that can perform the PMT at a speed of 720 frames per second (fps), enabling the construction of an efficient opto-electronic PMT pre-processor. Here, we present an experimental demonstration of a complete HOC that implements this technique to achieve real-time and ultra-fast SSRI target recognition for space situational awareness. For this demonstration, we make use of a modified version of the HOC that makes use of Joint Transform Correlation , thus rendering the system simpler and more compact.

physics.optics↗

arXiv2024

Sensitivity and Bandwidth of a Point-Source-Interferometry-based Inertial Measurement Unit Employing Large Momentum Transfer and Launched Atoms

We analyze theoretically the sensitivity of accelerometry and rotation sensing with a point source interferometer employing large momentum transfer (LMT) and present a design of an inertial measurement unit (IMU) that can measure rotation around and acceleration along each of the three axes. In this design, the launching technique is used to realize the LMT process without the need to physically change directions of the Raman pulses, thus significantly simplifying the apparatus. We also describe an explicit scheme for such an IMU.

quant-ph↗

arXiv2024

Implementation of large momentum transfer without swapping the directions of the Raman beams

Large momentum transfer (LMT) is an important technique for magnifying the phase shift accumulated in an atom interferometer. Existing approaches to implement Raman-transition-based LMT all involve physically swapping the propagation directions of the two counterpropagating Raman beams repeatedly, which could significantly complicate the experimental system. Here, we demonstrate a simpler approach for Raman-transition-based LMT that does not involve a physical swap of the directions of the Raman beams. In this approach, both Raman beams are retroreflected, and a Doppler shift induced by a bias velocity of the atoms is used to separate the transition frequencies of the two pairs of counterpropagating Raman beams. Therefore, an effective swap of the directions of the Raman beams can be achieved by shifting the relative frequency between the two Raman beams from the resonant frequency of one pair of the Raman beams to that of the other pair. We demonstrate the use of this technique for LMT-augmented accelerometry using atoms released from a magneto-optic trap.

quant-ph↗

arXiv2024

Algorithm for solving a pump-probe model for an arbitrary number of energy levels

We describe a generalized algorithm for evaluating the steady-state solution of the density matrix equation of motion, for the pump-probe scheme, when two fields oscillating at different frequencies couple the same set of atomic transitions involving an arbitrary number of energy levels, to an arbitrary order of the harmonics of the pump-probe frequency difference. We developed a numerical approach and a symbolic approach for this algorithm. We have verified that both approaches yield the same result for all cases studied, but require different computation time. The results are further validated by comparing them with the analytical solution of a two-level system to first order. We have also used both models to produce results up to the third order in the pump-probe frequency difference, for two-, three- and four-level systems. In addition, we have used this model to determine accurately, for the first time, the gain profile for a self-pumped Raman laser, for a system involving 16 Zeeman sublevels in the D1 manifold of 87Rb atoms. We have also used this model to determine the behavior of a single-pumped superluminal laser. In many situations involving the applications of multiple laser fields to atoms with many energy levels, one often makes the approximation that each field couples only one transition, because of the difficulty encountered in accounting for the effect of another field coupling the same transition but with a large detuning. The use of the algorithm presented here would eliminate the need for making such approximations, thus improving the accuracy of numerical calculations for such schemes.

quant-ph↗

arXiv2023

Strong frequency correlation and anti-correlation between a Raman laser and its pump laser for positive and negative dispersions

We show that the frequency of a Raman laser is highly correlated or anti-correlated with the frequency of the Raman pump laser, depending on whether the dispersion experienced by the Raman laser is positive or negative. For a subluminal laser, corresponding to a positive dispersion with a group index that is much larger than unity, the shift in its frequency is approximately the same as that in the Raman pump laser. In contrast, for a superluminal laser, corresponding to a negative dispersion with a group index that is close to zero, its frequency shifts in the direction opposite to that of the Raman pump lasers, and has an amplitude that is larger by a factor approximately equaling the inverse of the group index. These findings would play a critical role in determining the maximum achievable sensitivity of sensors employing such lasers, especially under conditions where the pump laser linewidth is broadened significantly beyond the Schawlow-Townes linewidth due to classical fluctuations.

quant-ph↗

arXiv2023

High-speed Opto-electronic Pre-processing of Polar Mellin Transform for Shift, Scale and Rotation Invariant Image Recognition at Record-Breaking Speeds

Space situational awareness demands efficient monitoring of terrestrial sites and celestial bodies, necessitating advanced target recognition systems. Current target recognition systems exhibit limited operational speed due to challenges in handling substantial image data. While machine learning has improved this scenario, highresolution images remain a concern. Optical correlators, relying on analog processes, provide a potential alternative but are hindered by material limitations. Recent advancements in hybrid opto-electronic correlators (HOC) have addressed such limitations, additionally achieving shift, scale, and rotation invariant (SSRI) target recognition through use of the polar Mellin transform (PMT). However, there are currently no techniques for obtaining the PMT at speeds fast enough to take advantage of the inherent speed of the HOC. To that end, we demonstrate an optoelectronic PMT pre-processor that can operate at record-breaking millisecond frame rates using commercially available components for use in an automated SSRI HOC image recognition system for space situational awareness.

eess.IV↗

arXiv2023

A generalized echo squeezing protocol with near-Heisenberg limit sensitivity and strong robustness against excess noise and variation in squeezing parameter

We present a generalized echo squeezing protocol (GESP) as a generalization of the Schrödinger cat state protocol (SCSP) with the value of the squeezing parameter being an arbitrary number rather than pi/2. We show analytically that over a broad range of the squeezing parameter the sensitivity reaches the Heisenberg limit (HL) within a factor of root-2. For a large number of particles, N, this plateau interval is almost the whole range from zero to pi/2, and the sensitivity is independent of the parity of N. Therefore, it is possible to operate a sensor over a wide interval of the squeezing parameter without changing the sensitivity. This is to be contrasted with the conventional echo squeezing protocol (CESP) which only works for a very small interval. In contrast to the CESP, the sensitivity of the GESP is close to the quantum Cramér-Rao bound over the whole range of the squeezing parameter. The enhancement in sensitivity for the GESP is due to a combination of two parameters: the phase magnification factor (PMF) and the noise amplification factor (NAF). As the value of the squeezing parameter increases, both PMF and NAF increase, keeping the ratio of PMF/NAF constant, yielding an enhancement of sensitivity at the HL within a factor of root-2. Thus, the robustness of the GESP against excess noise easily exceeds that of the CESP for a broad range of values of the squeezing parameter. As such, in the context of an experimental study, it should be possible to achieve a net enhancement in sensitivity higher than that for the CESP, under typical conditions where the excess noise exceeds the unsqueezed quantum projection noise. Finally, we consider the fragility of the GESP against collisions with background particles, and show how a balance between the fragility and the robustness against excess noise would in practice determine the optimal choice of parameters for the GESP.

quant-ph↗