arXiv subjects

Tanveer Ahmad

Publications and source records attributed to Tanveer Ahmad.

6 recordsLinked to original sources

arXiv2026

Schur--Horn bound on field-free molecular orientation at finite temperature

The maximum field-free orientation attainable from a \emph{thermal} molecular ensemble within a finite rotational subspace has not been characterised analytically. Here we derive a Schur--Horn-type upper bound on the field-free orientation $\avg{\cosθ}$ achievable by \emph{any} $M$-conserving unitary control acting on a Boltzmann ensemble truncated to rotational levels $J\le\Jmax$. The bound is the sum, over magnetic-quantum-number sectors, of the sorted Boltzmann weights paired with the sorted spectrum of $\cosθ$; it is purely kinematic, set by temperature, the rotational constant, and $\Jmax$ alone, and interpolates exactly between the zero-temperature subspace eigenvalue and a finite-temperature ceiling fixed by the rotational partition function. Benchmarked on LiH against the analytical $N$-subpulse resonant protocol of Hong \textit{et al.} [Phys.\ Rev.\ Research \textbf{7}, L012049 (2025)], it reveals three regimes: the protocol saturates the bound to within about $1.6\%$ for $T\le\SI{5}{\kelvin}$, loses roughly $10\%$ of its zero-temperature orientation at $T=B/\kB\approx\SI{10.8}{\kelvin}$, and leaves a $10$--$40\%$ gap above $\SI{10}{\kelvin}$. Optimising the subpulse areas and carrier phases within the fixed layout closes only $\approx7\%$ of that gap, the optimal phase offsets vanishing, which localises the dominant loss in the rigidity of the analytic layout rather than in the choice of areas or phases. The bound is a control-independent target for coherent-control design, applies unchanged to any linear polar molecule in a $^1Σ^+$ state, and is mapped across the $(\Jmax,T)$ plane.

quant-ph↗

arXiv2026

Tikhonov-regularised projected gradient flow for equality-constrained bilinear quantum control

We study a projection-type gradient flow for equality-constrained maximisation of a smooth bilinear control objective on $\mathcal{H}=L^2(0,T;\mathbb{R})$, eliminating Lagrange multipliers through an $(M{+}1)\times(M{+}1)$ moving Gram matrix $Γ(s)_{\ell\ell'}=\int_0^T S(t)\,c_\ell(s,t)\,c_{\ell'}(s,t)\,\mathrm{d}t$. The flow generates monotonic ascent in continuous time but becomes unstable on discretisation; existing implementations rely on heuristic step-size safeguards lacking rigorous justification. We close this gap by replacing $Γ$ with $Γ_{\varepsilon}:=Γ+\varepsilon^{2}I$ and prove: (i) an exact spectral identity giving $κ(Γ_{\varepsilon})=(σ_{\max}^{2}+\varepsilon^{2})/(σ_{\min}^{2}+\varepsilon^{2})$; (ii) objective monotonicity $\mathrm{d}J/\mathrm{d}s\ge 0$ for all $\varepsilon\ge 0$; (iii) constraint drift $|h_{m}-C_{m}|=\mathcal{O}(\varepsilon^{2})$ with a computable prefactor; (iv) convergence of the regularised trajectory to the unregularised one in $L^{2}(0,T)$ at rate $\mathcal{O}(\varepsilon^{2})$ under uniform invertibility of $Γ$; and (v) a discrete CFL criterion $Δs\,G\,\|Γ_{\varepsilon}^{-1}\|\leα<2$ guaranteeing objective monotonicity of the forward-Euler scheme up to $\mathcal{O}(Δs^{2})$ local truncation error. The theory is validated on a three-level bilinear benchmark for all-optical Bell-state preparation, where $κ(Γ)\in[10^{9},10^{11}]$, the predicted $\varepsilon^{2}$ rate is confirmed over eight decades, and moderate regularisation eliminates step rejections and reduces constraint drift by more than an order of magnitude at unchanged final fidelity.

quant-ph↗

arXiv2026

Noise-Robust Ultrafast Entanglement Generation in Rydberg Atoms via Quantum Optimal Control

We present a comprehensive theoretical analysis of ultrafast entanglement generation between two Rydberg-blockaded atoms, explicitly accounting for realistic laser noise. Using femtosecond Gaussian pulses as a baseline, we systematically evaluate Bell-state fidelity sensitivity to amplitude and phase noise across white, pink (1/f), and Ornstein-Uhlenbeck spectra using Monte Carlo ensemble simulations. Our results show that amplitude noise is well tolerated, with fidelities above 90% even at 30% noise levels, while phase noise is the primary limiting factor, causing fidelity to drop rapidly beyond about 1% noise amplitude. The spectral structure of the noise is also important: pink noise consistently causes less fidelity loss than white noise of the same amplitude. By applying quantum optimal control theory (QOCT) with the D-MORPH algorithm under multiple equality constraints, we obtain a double-pulse structure with a spectral notch that achieves approximately 99% fidelity in the noise-free case and maintains high fidelity under moderate amplitude noise. A breakdown threshold near 1% amplitude noise is identified, beyond which even optimized pulses cannot sustain coherent control. These results offer practical benchmarks for the development of ultrafast neutral-atom quantum processors operating in the femtosecond regime.

quant-ph↗

arXiv2023

SaLoBa: Maximizing Data Locality and Workload Balance for Fast Sequence Alignment on GPUs

Sequence alignment forms an important backbone in many sequencing applications. A commonly used strategy for sequence alignment is an approximate string matching with a two-dimensional dynamic programming approach. Although some prior work has been conducted on GPU acceleration of a sequence alignment, we identify several shortcomings that limit exploiting the full computational capability of modern GPUs. This paper presents SaLoBa, a GPU-accelerated sequence alignment library focused on seed extension. Based on the analysis of previous work with real-world sequencing data, we propose techniques to exploit the data locality and improve workload balancing. The experimental results reveal that SaLoBa significantly improves the seed extension kernel compared to state-of-the-art GPU-based methods.

cs.DB↗

arXiv2022

Benchmarking Apache Arrow Flight -- A wire-speed protocol for data transfer, querying and microservices

Moving structured data between different big data frameworks and/or data warehouses/storage systems often cause significant overhead. Most of the time more than 80\% of the total time spent in accessing data is elapsed in serialization/de-serialization step. Columnar data formats are gaining popularity in both analytics and transactional databases. Apache Arrow, a unified columnar in-memory data format promises to provide efficient data storage, access, manipulation and transport. In addition, with the introduction of the Arrow Flight communication capabilities, which is built on top of gRPC, Arrow enables high performance data transfer over TCP networks. Arrow Flight allows parallel Arrow RecordBatch transfer over networks in a platform and language-independent way, and offers high performance, parallelism and security based on open-source standards. In this paper, we bring together some recently implemented use cases of Arrow Flight with their benchmarking results. These use cases include bulk Arrow data transfer, querying subsystems and Flight as a microservice integration into different frameworks to show the throughput and scalability results of this protocol. We show that Flight is able to achieve up to 6000 MB/s and 4800 MB/s throughput for DoGet() and DoPut() operations respectively. On Mellanox ConnectX-3 or Connect-IB interconnect nodes Flight can utilize upto 95\% of the total available bandwidth. Flight is scalable and can use upto half of the available system cores efficiently for a bidirectional communication. For query systems like Dremio, Flight is order of magnitude faster than ODBC and turbodbc protocols. Arrow Flight based implementation on Dremio performs 20x and 30x better as compared to turbodbc and ODBC connections respectively.

cs.DC↗

arXiv2014

An improved accelerated frame slotted aloha (afsa) algorithm for tag collision in rfid

The efficiency of tag identification in an RFID system can be low down due to the tag collision problems. the tag collision problem occurs when a reader try to read multiple tags in an interrogation zone. as a result the reader does not identify the tag correctly. that causes a loss of information or data interference. to solve such kind of issues a series of aloha based algorithm and binary search algorithm have beed proposed. the most simple popular and good giving performance algorithm are aloha based anti-collision algorithms. in this paper we present a new variation in accelerated slotted aloha afsa. our proposed algorithm by using the bitmaps and avoids wastages in bit times due to idleness and collided slots reduce the tag reading time. the simulation result shows that afsa can significantly reduce the average tag reading time with respect to the base protocols and achieve high tag reading rates under both static and mobile setting.

cs.NI↗