About

Zeeshan Ahmed is an Associate Professor of Particle Physics and Astrophysics at Stanford University and SLAC National Accelerator Laboratory. He is an observational cosmologist and experimental physicist specializing in building ultra-low-noise detectors using superconducting and quantum sensing techniques, which are employed in experiments and instrumentation for cosmology. His research primarily investigates the inflation paradigm of standard cosmology through the study of the cosmic microwave background (CMB). Recently, he has become interested in utilizing the weak lensing of the CMB in conjunction with galaxy surveys to analyze the growth of large-scale structures in the universe. Zeeshan Ahmed received his PhD in particle astrophysics from Caltech in 2012, focusing on the direct detection of WIMP dark matter with the CDMS-II experiment. He then shifted his research efforts to searching for inflation signals with the CMB. After serving as a postdoctoral scholar at Stanford until 2015, he was appointed as a Wolfgang Panofsky Fellow at SLAC National Accelerator Laboratory. In 2017, he was awarded a DOE Office of Science Early Career Award to develop new signal transduction and superconducting multiplexing techniques for next-generation CMB cameras. He was appointed as a Lead Scientist at SLAC in 2020 and became an Associate Professor at Stanford and SLAC in 2023. Additionally, he serves as the CMB department head in the Fundamental Physics Directorate at SLAC and manages scientific projects related to the development of superconducting and quantum sensors at SLAC's Detector Microfabrication Facility.

Research topics

• Optics
• Physics
• Astronomy
• Astrophysics
• Computer Science
• Acoustics
• Mathematics
• Telecommunications
• Geology
• Remote sensing
• Algorithm

Selected publications

• CMB-S4: Foreground-Cleaning Pipeline Comparison for Measuring Primordial Gravitational Waves

  ArXiv.org · 2025-02-06

  preprintOpen access

  We compare multiple foreground-cleaning pipelines for estimating the tensor-to-scalar ratio, $r$, using simulated maps of the planned CMB-S4 experiment within the context of the South Pole Deep Patch. To evaluate robustness, we analyze bias and uncertainty on $r$ across various foreground suites using map-based simulations. The foreground-cleaning methods include: a parametric maximum likelihood approach applied to auto- and cross-power spectra between frequency maps; a map-based parametric maximum-likelihood method; and a harmonic-space internal linear combination using frequency maps. We summarize the conceptual basis of each method to highlight their similarities and differences. To better probe the impact of foreground residuals, we implement an iterative internal delensing step, leveraging a map-based pipeline to generate a lensing $B$-mode template from the Large Aperture Telescope frequency maps. Our results show that the performance of the three approaches is comparable for simple and intermediate-complexity foregrounds, with $σ(r)$ ranging from 3 to 5 $\times 10^{-4}$. However, biases at the $1-2σ$ level appear when analyzing more complex forms of foreground emission. By extending the baseline pipelines to marginalize over foreground residuals, we demonstrate that contamination can be reduced to within statistical uncertainties, albeit with a pipeline-dependent impact on $σ(r)$, which translates to a detection significance between 2 and 4$σ$ for an input value of $r = 0.003$. These findings suggest varying levels of maturity among the tested pipelines, with the auto- and cross-spectra-based approach demonstrating the best stability and overall performance. Moreover, given the extremely low noise levels, mutual validation of independent foreground-cleaning pipelines is essential to ensure the robustness of any potential detection.

  PublisherOA PDFDOI

• CMB-S4: Foreground-cleaning Pipeline Comparison for Measuring Primordial Gravitational Waves

  The Astrophysical Journal · 2025-10-28 · 7 citations

  articleOpen access

  Abstract We compare multiple foreground-cleaning pipelines for estimating the tensor-to-scalar ratio, r , using simulated maps of the planned CMB-S4 experiment within the context of the South Pole Deep Patch. To evaluate robustness, we analyze bias and uncertainty on r across various foreground suites using map-based simulations. The foreground-cleaning methods include: a parametric maximum likelihood approach applied to auto- and cross-power spectra between frequency maps; a map-based parametric maximum-likelihood method; and a harmonic-space internal linear combination using frequency maps. We summarize the conceptual basis of each method to highlight their similarities and differences. To better probe the impact of foreground residuals, we implement an iterative internal delensing step, leveraging a map-based pipeline to generate a lensing B -mode template from the large aperture telescope frequency maps. Our results show that the performance of the three approaches is comparable for simple and intermediate-complexity foregrounds, with σ ( r ) ranging from 3–5 ×10 −4 . However, biases at the 1 σ –2 σ level appear when analyzing more complex forms of foreground emission. By extending the baseline pipelines to marginalize over foreground residuals, we demonstrate that contamination can be reduced to within statistical uncertainties, albeit with a pipeline-dependent impact on σ ( r ), which translates to a detection significance between 2 σ and 4 σ for an input value of r = 0.003. These findings suggest varying levels of maturity among the tested pipelines, with the auto- and cross-spectra-based approach demonstrating the best stability and overall performance. Moreover, given the extremely low noise levels, mutual validation of independent foreground-cleaning pipelines is essential to ensure the robustness of any potential detection.

  PublisherDOI

• Demonstration of a 1820 channel multiplexer for transition-edge sensor bolometers

  Applied Physics Letters · 2025-10-13 · 3 citations

  article

  The scalability of most transition-edge sensor arrays is limited by the multiplexing technology, which combines their signals over a reduced number of wires and amplifiers. In this Letter, we present and demonstrate a multiplexer design optimized for transition-edge sensor bolometers with 1820 sensors per readout unit, a factor of two more than the previous state-of-the-art. The design is optimized for cosmic microwave background imaging applications, and it builds on previous microwave superconducting quantum interference device multiplexers by doubling the available readout bandwidth to the full 4–8 GHz octave. Evaluating the key performance metrics of yield, sensitivity, and crosstalk through laboratory testing, we find an end-to-end operable detector yield of 78%, a typical nearest-neighbor crosstalk amplitude of ∼0.4%, and a median white noise level of 83 pA/Hz due to the multiplexer, corresponding to an estimated contribution of 4% to the total system noise for a ground-based cosmic microwave background telescope. Additionally, we identify a possible path toward reducing resonator loss for future designs with reduced noise. We expect these developments to alleviate the system complexity, cryogenic requirements, and cost of future large arrays of low temperature detectors.

  PublisherDOI

• Demonstration of a 1820 channel multiplexer for transition-edge sensor bolometers

  arXiv (Cornell University) · 2025-07-15 · 1 citations

  preprintOpen access

  The scalability of most transition-edge sensor arrays is limited by the multiplexing technology which combines their signals over a reduced number of wires and amplifiers. In this Letter, we present and demonstrate a multiplexer design optimized for transition-edge sensor bolometers with 1820 sensors per readout unit, a factor of two more than the previous state-of-the-art. The design is optimized for cosmic microwave background imaging applications, and it builds on previous microwave superconducting quantum interference device multiplexers by doubling the available readout bandwidth to the full 4-8 GHz octave. Evaluating the key performance metrics of yield, sensitivity, and crosstalk through laboratory testing, we find an end-to-end operable detector yield of 78%, a typical nearest-neighbor crosstalk amplitude of ~0.4%, and a median white noise level of 83 pA/rtHz due to the multiplexer, corresponding to an estimated contribution of 4% to the total system noise for a ground-based cosmic microwave background telescope. Additionally, we identify a possible path toward reducing resonator loss for future designs with reduced noise. We expect these developments to alleviate the system complexity, cryogenic requirements, and cost of future large arrays of low temperature detectors.

  PublisherOA PDFDOI

• Global Challenges of Enteric Fever: Gaps, Hurdles, and Hope

  Journal of Science Technology Education Art and Medicine · 2025-08-30 · 1 citations

  articleOpen access1st authorCorresponding

  Enteric fever, caused by Salmonella enterica serovars Typhi and Paratyphi, remains a pressing global health challenge. In 2021, the disease affected an estimated 9.3 million people and caused more than 100,000 deaths worldwide, with the greatest burden concentrated in South Asia and sub-Saharan Africa, particularly among children younger than five years. 1 The clinical overlap with other febrile illnesses continues to complicate timely diagnosis. 2 Simultaneously, the relentless spread of multidrug-resistant strains of S. Typhi threatens to erode existing treatment options and undermines global health security. 3 Despite decades of recognition, several entrenched challenges impede progress. Diagnostic capacity in endemic regions remains profoundly limited. 4 Blood culture, the current standard, suffers from poor sensitivity and requires infrastructure that is often absent. 5 Chronic carriers frequently go undetected, perpetuating community transmission. At the same time, antimicrobial resistance (AMR) has escalated sharply, diminishing the effectiveness of first-line antibiotics and leaving clinicians with dwindling therapeutic options. Typhoid conjugate vaccines (TCVs) represent a scientific success story: they are safe, effective, and recommended by the World Health Organization (WHO) for use in endemic regions. 5 Yet, vaccine uptake lags far behind need. Delays in adoption are linked to competing health priorities, limited political will, weak immunization systems, and inadequate public awareness. 6, 7 This mismatch between evidence and implementation highlights a systemic failure of global health governance. The epidemiology of enteric fever is inextricably linked to structural inequities. Poor sanitation, unsafe water, and fragile health systems perpetuate transmission and hinder control. 8 Underinvestment is striking, relative to its burden, and enteric fever remains neglected in global health financing. While donor interest surges for high-profile epidemics, typhoid continues to struggle for visibility. These underfunding hampers diagnostics, vaccine rollout, and research into novel therapies. Addressing enteric fever demands coordinated, multi-layered interventions. First, strengthening diagnostic infrastructure is imperative. Affordable, rapid diagnostic tests and molecular assays, alongside expanded access to blood cultures, would enable earlier detection and identification of asymptomatic carriers. 4 Second, robust antimicrobial stewardship programs and urgent investment in new therapeutic development are required to counter the accelerating AMR crisis. 4 Third, widespread deployment of TCVs should be prioritized. 9 Evidence shows that routine infant immunization, combined with catch-up campaigns, is both highly cost-effective and capable of substantially reducing incidence. 10 Finally, sustainable improvements in water, sanitation, and hygiene (WASH) infrastructure are fundamental for long-term prevention. National governments, multilateral agencies, and global health donors must act decisively. Endemic countries should integrate TCVs into routine immunization schedules without delay. International partners should provide financial and technical support for vaccine rollouts, laboratory strengthening, and WASH projects. Policymakers must also recognize that the fight against enteric fever is inseparable from broader goals of equity and health system resilience. Further research, particularly into surveillance, novel diagnostics, and innovative therapies, remains critical. But evidence alone will not suffice. What is required is political commitment commensurate with the scale of the problem. Without urgent, coordinated action, the global community risks perpetuating a preventable disease that disproportionately affects the world’s most vulnerable. With sustained investment and unified resolve, enteric fever can be controlled and ultimately consigned to history.

  PublisherDOI

• Simulating quantum collision models with Hamiltonian simulations using early fault-tolerant quantum computers

  Physical review. A/Physical review, A · 2025-08-19 · 2 citations

  articleOpen access

  We develop randomized quantum algorithms to simulate quantum collision models, also known as repeated interaction schemes, which provide a rich framework to model various open-system dynamics. The underlying technique involves composing time evolutions of the total (system, bath, and interaction) Hamiltonian and intermittent tracing out the environment degrees of freedom. This results in a unified framework where any near-term Hamiltonian simulation algorithm can be incorporated to implement an arbitrary number of such collisions on early fault-tolerant quantum computers: we do not assume access to specialized oracles such as block encodings and minimize the number of ancilla qubits needed. In particular, using the correspondence between Lindbladian evolution and completely positive trace-preserving maps arising out of memoryless collisions, we provide an end-to-end quantum algorithm for simulating Lindbladian dynamics. For a system of $n$-qubits, we exhaustively compare the circuit depth needed to estimate the expectation value of an observable with respect to the reduced state of the system after time $t$ while employing different near-term Hamiltonian simulation techniques, requiring at most $n+2$ qubits in all. We compare the cnot gate counts of the various approaches for estimating the transverse field magnetization of a 10-qubit XX-Heisenberg spin chain under amplitude damping. Finally, we also develop a framework to efficiently simulate an arbitrary number of memory-retaining collisions, i.e., where environments interact, leading to non-Markovian dynamics. Overall, our methods can leverage quantum collision models for both Markovian and non-Markovian dynamics on early fault-tolerant quantum computers, shedding light on the advantages and limitations of simulating open systems dynamics using this framework.

  PublisherOA PDFDOI

• Simons Observatory: Characterization of the Large Aperture Telescope Receiver

  ArXiv.org · 2025-01-16 · 1 citations

  preprintOpen access

  The Simons Observatory (SO) is a ground-based cosmic microwave background (CMB) survey experiment that currently consists of three 0.42m small-aperture telescopes (SATs) and one 6m large-aperture telescope (LAT), located at an elevation of 5200m in the Atacama Desert in Chile. At the LAT's focal plane, SO will install >62,000 transition-edge sensor detectors across 13 optics tubes (OTs) within the Large Aperture Telescope Receiver (LATR), the largest cryogenic camera ever built to observe the CMB. Here we report on the validation of the LATR in the laboratory and the subsequent dark testing and validation within the LAT. We show that the LATR meets cryogenic, optical, and detector specifications required for high-sensitivity measurements of the CMB. At the time of writing, the LATR is installed in the LAT with six OTs (corresponding to >31,000 detectors), and the LAT mirrors and remaining seven OTs are undergoing development.

  PublisherOA PDFDOI

• Assessing Occupational Health Hazards Among Solid Waste Workers in a Developing Country: A Cross-sectional Mixed-methods Study From a Metropolitan City in India

  American Journal of Respiratory and Critical Care Medicine · 2025-05-01

  article

  Abstract Rationale The world generates approximately 2.01 billion tonnes of solid waste annually, projected to rise to 3.40 billion tonnes by 2050. This growth significantly strains waste management systems, particularly in developing countries like India. In Hyderabad, Telangana, municipal solid waste (MSW) workers play a vital role in waste collection, sorting, and disposal but face severe occupational health risks. This study aims to investigate the health hazards and safety compliance issues among MSW workers, providing insights to enhance health and safety measures in the sector. Methods This observational, cross-sectional study employed a mixed-methods approach involving 150 MSW workers from various roles, including waste collection, sorting, and transportation. Workers were selected through convenience sampling, focusing on those with at least six months of experience. Data collection utilized a pre-designed, pre-tested questionnaire covering demographics, work environment, safety practices, and health systems. Direct interviews were conducted in participants’ local language, and observational assessments of work conditions and PPE compliance were performed. Ethical approval was granted by the Institutional Review Board (IRB), with informed consent obtained from all participants to ensure confidentiality and the right to withdraw at any time. Data analyzed using SPSS and chi-square tests to explore correlations between job roles and health risks. Results The findings revealed diverse age and gender distributions, body mass indices (BMI), work types, and years of experience. Among the workers surveyed, 66% reported physical injuries during waste handling, but only 29% reported these injuries to supervisors, mainly due to a lack of awareness and the perception that injuries were not serious. Health assessments indicated a high prevalence of health hazards: 90% experienced musculoskeletal symptoms, 67% had dermatological issues, 66% reported respiratory symptoms, and 56% faced gastrointestinal symptoms. A chi-square analysis showed a significant relationship between injury frequency and PPE usage (chi-square value = 13.21, p = 0.03), highlighting that inconsistent PPE use contributes to higher injury rates. Health risks varied significantly by job role, with garbage collectors and street sweepers facing more severe symptoms than waste transporters and recycling sorters. While 66% of workers reported receiving vaccinations, many perceived inadequate access to vaccination programs. Conclusion These findings underscore serious health risks among MSW workers in a developing country, driven by inconsistent PPE use, insufficient training, and limited healthcare access. Implementing enhanced health and safety protocols, improving access to PPE, and establishing targeted health programs are essential to safeguard this workforce in the face of growing urban challenges.

  PublisherDOI

• Simons Observatory: Characterization of the Large Aperture Telescope Receiver

  The Astrophysical Journal Supplement Series · 2025-07-17 · 3 citations

  articleOpen access

  Abstract The Simons Observatory (SO) is a ground-based cosmic microwave background (CMB) survey experiment that currently consists of three 0.42 m small-aperture telescopes and one 6 m large-aperture telescope (LAT), located at an elevation of 5200 m in the Atacama Desert in Chile. At the LAT’s focal plane, SO will install >62,000 transition-edge sensor detectors across 13 optics tubes (OTs) within the Large Aperture Telescope Receiver (LATR), the largest cryogenic camera ever built to observe the CMB. Here we report on the validation of the LATR in the laboratory and the subsequent dark testing and validation within the LAT. We show that the LATR meets cryogenic, optical, and detector specifications required for high-sensitivity measurements of the CMB. At the time of writing, the LATR is installed in the LAT with six OTs (corresponding to >31,000 detectors), and the LAT mirrors and remaining seven OTs are undergoing development.

  PublisherDOI

• New high-statistics measurement of the $π^0 \to e^+e^-γ$ Dalitz decay at the Mainz Microtron

  ArXiv.org · 2025-12-03

  preprintOpen access

  The Dalitz decay $π^0 \to e^+e^-γ$ has been measured with the highest statistical accuracy obtained so far in the $γp\to π^0 p$ reaction with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The value of the slope parameter for the $π^0$ electromagnetic transition form factor, $a_π=0.0315\pm 0.0026_{\mathrm{stat}}\pm 0.0010_{\mathrm{syst}}$, is obtained from the analysis of $2.4\times10^6$ $π^0 \to e^+e^-γ$ observed decays. Within experimental uncertainties, it is in agreement with existing measurements and theoretical calculations, with its own uncertainty being smaller than previous results based on the analysis of $π^0\to e^+e^-γ$ decays.

  PublisherOA PDFDOI

Frequent coauthors

• K. D. Irwin

  529 shared

• A. Cukierman

  Menlo School

  334 shared

• C. L. Kuo

  294 shared

• K. W. Yoon

  Stanford University

  289 shared

• K. L. Thompson

  Stanford University

  270 shared

• W. L. K. Wu

  238 shared

• R. W. Ogburn

  SLAC National Accelerator Laboratory

  203 shared

• B. A. Benson

  Netherlands Institute for Radio Astronomy

  203 shared

Labs

• Zeeshan Ahmed's LabPI

Awards & honors

• Wolfgang Panofsky Fellow at SLAC National Accelerator Labora…
• DOE Office of Science Early Career Award (2017)