About

Karl van Bibber is a professor in the Department of Nuclear Engineering at UC Berkeley, with a background in physics and mathematics from MIT, where he earned his B.S. degrees in 1972 and his Ph.D. in physics in 1976. His research interests encompass nuclear physics, particle physics, particle astrophysics, nuclear instrumentation, and accelerator science and technology. Van Bibber has held numerous leadership roles, including Chairman of the Department of Nuclear Engineering at UC Berkeley since 2022, and previously served as Executive Associate Dean and Associate Dean for Research in the College of Engineering. He has also been involved with the Nuclear Science Division at Lawrence Berkeley National Laboratory and has held significant positions at Lawrence Livermore National Laboratory, including Senior Physicist, Group Leader, and Chief Scientist. His career includes academic appointments at Stanford University and research positions at Lawrence Berkeley National Laboratory. Van Bibber's contributions have been recognized through various awards and honors, including election as a Fellow of the American Association for the Advancement of Science and the American Physical Society, as well as awards from the Department of Energy and Lawrence Livermore National Laboratory. His work has contributed to advancements in nuclear and particle physics, with notable research on dark matter axions, neutrons for geochronology, and CP violation in meson systems.

Research topics

• Computer Science
• Physics
• Statistics
• Theoretical physics
• Optics
• Engineering
• Astrophysics
• Astronomy
• Nuclear physics
• Particle physics
• Mathematics

Selected publications

• Practical photonic bandgap structures for high frequency axion haloscopes

  Review of Scientific Instruments · 2025-09-01 · 1 citations

  articleSenior author

  Current and future searches for dark matter axions, based on their resonant conversion to photons in a magnetic field, span many orders of magnitude. A major impediment to designing resonators at the high end of this range, 5 GHz and above, is the proliferation of TE modes, which overwhelm and hybridize with the TM010 mode to which the axion couples, making the search impossible. We demonstrate that a photonic bandgap structure can be designed that completely suppresses the TE spectrum, even reducing the number of lattice periods to two or one and violating perfect lattice symmetry. This allows tunable resonators to be designed in a convenient, volumetrically efficient circular geometry thus enabling future searches in the post-inflation axion mass range.

  PublisherDOI

• Dark Matter Axion Search with HAYSTAC Phase II

  Physical Review Letters · 2025-04-18 · 22 citations

  articleOpen access

  This Letter reports new results from the HAYSTAC experiment's search for dark matter axions in our galactic halo. It represents the widest search to date that utilizes squeezing to realize subquantum limited noise. The new results cover 1.71 μeV of newly scanned parameter space in the mass ranges 17.28-18.44 μeV and 18.71-19.46 μeV. No statistically significant evidence of an axion signal was observed, excluding couplings |g_{γ}|≥2.75×|g_{γ}^{KSVZ}| and |g_{γ}|≥2.96×|g_{γ}^{KSVZ}| at the 90% confidence level over the respective region. By combining this data with previously published results using HAYSTAC's squeezed state receiver, a total of 2.27 μeV of parameter space has now been scanned between 16.96-19.46 μeVμ eV, excluding |g_{γ}|≥2.86×|g_{γ}^{KSVZ}| at the 90% confidence level. These results demonstrate the squeezed state receiver's ability to probe axion models over a significant mass range while achieving a scan rate enhancement relative to a quantum-limited experiment.

  PublisherOA PDFDOI

• Search for Dark Photons between 16.96--19.52 $μ$eV with the HAYSTAC Experiment

  arXiv (Cornell University) · 2025-10-17

  preprintOpen access

  We report dark photon results from HAYSTAC Phase II using data from previously reported axion searches. Additionally, we present an analysis of an unpublished dataset covering a region between 19.46--19.52 $μ$eV. This region overlaps with a recently reported dark photon signal at 19.5 $μ$eV with a kinetic coupling strength of $|χ_{\text{rand}}| \simeq 6.5 \times 10^{-15}$ resulting from a reanalysis of previously published data from the TASEH collaboration. Given HAYSTAC's sensitivity, if such a signal were present, it would have appeared as a large $17.1σ$ excess above the noise. However, no such signal was observed. We thus exclude couplings $|χ_{\text{rand}}|\geq 4.90\times10^{-15}$ at the 90\% confidence level over the newly reported region. In addition, using our previously reported axion data, we exclude couplings $|χ_{\text{rand}}|\geq2.90\times 10^{-15}$ between 16.96--19.46 $μ$eV at the 90\% confidence level.

  PublisherOA PDFDOI

• A Model-independent Radio Telescope Dark Matter Search in the <i>L</i> and <i>S</i> Bands

  The Astrophysical Journal Letters · 2025-04-30

  articleOpen accessSenior author

  Abstract Ultralight bosonic dark matter in its most general form can be detected through its decay or annihilation to a quasimonochromatic radio line. Assuming only that this line is consistent with the most general properties of the expected phase space of our Milky Way halo, we have developed and carried out a novel model-independent search for dark matter in the L and S bands. More specifically, the search selects for a line that exhibits a Doppler shift with position according to the solar motion through a static halo and similarly varies in intensity with position with respect to the Galactic center. Over the combined L - and S -band range 1020–2700 MHz, radiative annihilation of dark matter is excluded above 〈 σv 〉 ≈ 10 −30 cm 3 s −1 , and for decay above λ ≈ 10 −32 s −1 .

  PublisherDOI

• Noise limits for dc SQUID readout of high-<i>Q</i> resonators below 300 MHz

  Journal of Applied Physics · 2025-09-04

  articleOpen access

  We present the limits on noise for the readout of cryogenic high-Q resonators using dc Superconducting Quantum Interference Devices (SQUIDs) below 300 MHz. This analysis uses realized first-stage SQUIDs (previously published), whose performance is well described by Tesche–Clarke (TC) theory, coupled directly to the resonators. We also present data from a prototype second-stage dc SQUID array designed to couple to this first-stage SQUID as a follow-on amplifier with high system bandwidth. This analysis is the first full consideration of dc SQUID noise performance referred to a high-Q resonator over this frequency range and is presented relative to the standard quantum limit. We include imprecision, backaction, and backaction–imprecision noise correlations from TC theory, the noise contributed by the second-stage SQUIDs, wiring, and preamplifiers, and optimizations for both on-resonance measurements and off-resonance scan sensitivity. This architecture has modern relevance due to the increased interest in axion searches and the requirements of the DMRadio-m3 axion search, which uses dc SQUIDs in this frequency range.

  PublisherDOI

• Electromagnetic modeling and science reach of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mtext>DMRadio-</mml:mtext><mml:msup><mml:mrow><mml:mi mathvariant="normal">m</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math>

  Physical review. D/Physical review. D. · 2025-09-02 · 1 citations

  articleOpen access

  <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mrow><a:mtext>DMRadio-</a:mtext><a:msup><a:mrow><a:mi mathvariant="normal">m</a:mi></a:mrow><a:mrow><a:mn>3</a:mn></a:mrow></a:msup></a:mrow></a:math> is an experimental search for dark matter axions. It uses a solenoidal dc magnetic field to convert an axion dark-matter signal to an ac electromagnetic response in a coaxial copper pickup. The current induced by this axion signal is measured by dc SQUIDs. <d:math xmlns:d="http://www.w3.org/1998/Math/MathML" display="inline"><d:mrow><d:mtext>DMRadio-</d:mtext><d:msup><d:mrow><d:mi mathvariant="normal">m</d:mi></d:mrow><d:mrow><d:mn>3</d:mn></d:mrow></d:msup></d:mrow></d:math> is designed to be sensitive to Kim-Shifman-Vainshtein-Zakharov (KSVZ) and Dine-Fischler-Srednicki-Zhitnisky (DFSZ) QCD axion models in the 10–200 MHz (<g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:mrow><g:mn>41</g:mn><g:mtext> </g:mtext><g:mtext> </g:mtext><g:mi>neV</g:mi><g:mo>/</g:mo><g:msup><g:mi>c</g:mi><g:mn>2</g:mn></g:msup><g:mi>–</g:mi><g:mrow><g:mn>0.83</g:mn><g:mtext> </g:mtext><g:mtext> </g:mtext><g:mi mathvariant="normal">μ</g:mi><g:mi>eV</g:mi><g:mo>/</g:mo><g:msup><g:mi>c</g:mi><g:mn>2</g:mn></g:msup></g:mrow></g:mrow></g:math>) range, and to axions with <j:math xmlns:j="http://www.w3.org/1998/Math/MathML" display="inline"><j:msub><j:mi>g</j:mi><j:mrow><j:mi>a</j:mi><j:mi>γ</j:mi><j:mi>γ</j:mi></j:mrow></j:msub><j:mo>=</j:mo><j:msub><j:mi>g</j:mi><j:mrow><j:mi>a</j:mi><j:mi>γ</j:mi><j:mi>γ</j:mi><j:mo>,</j:mo><j:mrow><j:mi>DFSZ</j:mi></j:mrow></j:mrow></j:msub><j:mo stretchy="false">(</j:mo><j:mn>30</j:mn><j:mtext> </j:mtext><j:mtext> </j:mtext><j:mi>MHz</j:mi><j:mo stretchy="false">)</j:mo><j:mo>=</j:mo><j:mn>1.87</j:mn><j:mo>×</j:mo><j:msup><j:mn>10</j:mn><j:mrow><j:mo>−</j:mo><j:mn>17</j:mn></j:mrow></j:msup><j:mtext> </j:mtext><j:mtext> </j:mtext><j:msup><j:mrow><j:mi>GeV</j:mi></j:mrow><j:mrow><j:mo>−</j:mo><j:mn>1</j:mn></j:mrow></j:msup></j:math> over 5–30 MHz as an extended goal. In this work, we present the electromagnetic modeling of the response of the experiment to an axion signal over the full frequency range of <n:math xmlns:n="http://www.w3.org/1998/Math/MathML" display="inline"><n:mrow><n:mtext>DMRadio-</n:mtext><n:msup><n:mrow><n:mi mathvariant="normal">m</n:mi></n:mrow><n:mrow><n:mn>3</n:mn></n:mrow></n:msup></n:mrow></n:math>, which extends from the low-frequency, lumped-element limit to a regime where the axion Compton wavelength is only a factor of 2 larger than the detector size. With these results, we determine the live time and sensitivity of the experiment. The primary science goal of sensitivity to DFSZ axions across 30–200 MHz can be achieved with a <q:math xmlns:q="http://www.w3.org/1998/Math/MathML" display="inline"><q:mn>3</q:mn><q:mi>σ</q:mi></q:math> live scan time of 2.9 years.

  PublisherOA PDFDOI

• Dark Matter Axion Search with HAYSTAC Phase II

  arXiv (Cornell University) · 2024-09-13 · 1 citations

  preprintOpen access

  This Letter reports new results from the HAYSTAC experiment's search for dark matter axions in our galactic halo. It represents the widest search to date that utilizes squeezing to realize sub-quantum limited noise. The new results cover 1.71 $μ$eV of newly scanned parameter space in the mass ranges 17.28-18.44 $μ$eV and 18.71-19.46 $μ$eV. No statistically significant evidence of an axion signal was observed, excluding couplings $|g_γ|\geq$ 2.75$\times$$|g_γ^{\text{KSVZ}}|$ and $|g_γ|\geq$ 2.96$\times$$|g_γ^{\text{KSVZ}}|$ at the 90$\%$ confidence level over the respective region. By combining this data with previously published results using HAYSTAC's squeezed state receiver, a total of 2.27 $μ$eV of parameter space has now been scanned between 16.96-19.46 $μ$eV, excluding $|g_γ|\geq$ 2.86$\times$$|g_γ^{\text{KSVZ}}|$ at the 90$\%$ confidence level. These results demonstrate the squeezed state receiver's ability to probe axion models over a significant mass range while achieving a scan rate enhancement relative to a quantum-limited experiment.

  PublisherOA PDFDOI

• Practical photonic band gap structures for high frequency axion haloscopes

  arXiv (Cornell University) · 2024-11-28

  preprintOpen accessSenior author

  Current and future searches for dark matter axions, based on their resonant conversion to photons in a magnetic field, span many orders of magnitude. A major impediment to designing resonators at the high end of this range, 5 GHz and above, is the proliferation of TE modes, which overwhelm and hybridize with the TM010 mode to which the axion couples, making the search impossible. We demonstrate that a photonic band gap structure can be designed that completely suppresses the TE spectrum, even reducing the number of lattice periods to two or one, and violating perfect lattice symmetry. This allows tunable resonators to be designed in a convenient, volumetrically efficient circular geometry thus enabling future searches in the post-inflation axion mass range.

  PublisherOA PDFDOI

• A tunable photonic band gap resonator for axion dark matter searches

  arXiv (Cornell University) · 2024-08-07

  preprintOpen accessSenior author

  Axions are a well-motivated dark matter candidate particle. Haloscopes aim to detect axions in the galactic halo by measuring the photon signal resulting from axions interacting with a strong magnetic field. Existing haloscopes are primarily targeting axion masses which produce microwave-range photons and rely on microwave resonators to enhance the signal power. Only a limited subset of resonator modes are useful for this process, and current cylindrical-style cavities suffer from mode mixing and crowding from other fundamental modes. The majority of these modes can be eliminated by using photonic band gap (PBG) resonators. The band gap behavior of these structures allows for a resonator with mode selectivity based on frequency. We present results from the first tunable PBG resonator, a proof-of-concept design with a footprint compatible with axion haloscopes. We have thoroughly characterized the tuning range of two versions of the structure and report the successful confinement of the operating TM$_{010}$ mode and the elimination of all TE modes within the tuning range.

  PublisherOA PDFDOI

• Correction to: The Search for Ultralight Bosonic Dark Matter

  2023-01-01 · 4 citations

  book-chapterOpen accessSenior author

  The original version of this chapter was published with incorrect text on page 48 last paragraph 8th and 9th lines

  PublisherOA PDFDOI

Recent grants

• Collaborative Research: ADMX-HF Early Start

  NSF · $332k · 2013–2016

• Collaborative Research: ADMX-HF Extreme Axion Experiment

  NSF · $421k · 2016–2020

• Collaborative Research: HAYSTAC Sub-Quantum

  NSF · $486k · 2019–2022

Frequent coauthors

• I. Scott

  115 shared

• J. Button‐Shafer

  Lawrence Berkeley National Laboratory

  114 shared

• O. Hamon

  Sorbonne Université

  103 shared

• H. Briand

  103 shared

• L. Roos

  Laboratoire de Physique Nucléaire et de Hautes Énergies

  102 shared

• T. Himel

  SLAC National Accelerator Laboratory

  102 shared

• M. Carpinelli

  102 shared

• M. Benayoun

  Université Paris Cité

  102 shared

Awards & honors

• Navy Superior Civilian Service Award (2012)
• Elected Fellow of the American Association for the Advanceme…
• DOE Deputy Secretary’s Award for the B Factory, on behalf of…
• LLNL S&T Award, BaBar team for discovery of CP-violation in…
• LLNL Director’s Distinguished Performance Award for the B Fa…