Apr 2025-Jun 2025

Attendees: RL, MK, SD, CSW, SS, JB, AH, PB, BZ, SZ, GPC, NT, BL, IH, EM, Jeffrey, TC, ÉM, 

Announcements:

Agenda:

• Sketchy documentation for mesh electric fields is available (waiting for Jesse to discuss – may move to next biweekly technical meeting so he can hear)
• Presentation of materials tutorial by Caitlyn/Israel
  • Caitlyn: tutorial on using phonopy to get DOS for phonons.
    • Currently on her own github, but plan to make a Jira ticket, new branch, and pull request to integrate this into G4CMP's tools section
  • Israel: most of the way through a program to 
• AOB
• Iman's talk about charge transport (why oblique acceleration of electrons in Ge?) : 
  • Part 2 
  • Part 3

Attendees: RL, JY, SS, JL, Samir Banik, ÉM, Anna Huynh, CSW, JB, TC, KO

Announcements:

Agenda:

• Jesse: 
  • Data taken along 2 orientations of a lattice for Si – indicate 2 different velocities that should be reproducible in G4CMP

    • https://arxiv.org/pdf/1807.07986

  • Should have different velocities but don't see this in sims that he's running – what might be wrong? Will chat with Émile to debug
  • Also, what does a standard mesh field file look like?
    • What does the format of the external file look like? 
    • Will poke Mike to ask about specifics since nobody here uses these all that much.
  • ÉM: Able to reproduce drift speed for 001 orientation?
  • What is it that you're rotating with the macro command you're using?
  • Will try modifying code as a cross-check to using macro commands
• AOB

Attendees: RL, MK, John Batarkeh, CSW, Annah Huynh, JY, NT, BZ, SZ, ÉM, IH, Kiichi Okubo, JL, SS, MJ, TC

Announcements:

• Last meeting, showed surface mode displacement code, starting now to look at second half of problem, which is nonlinear decay at surface, to get bulk reflection + surface mode
  • MFPs for surface mode, etc.
  • Do we lose energy over seconds or do phonons return
  • Don't want to try to do microscopic detail that G4 does with optics, but will have specular vs. diffuse 
  • Will defer to Nolan for details on how to model scattering centers for bulk/surface conversion
  • Doing just surface transport introduces interesting time shift in SCDMS data
    • Long enough that we can see 5-10 μs delays in data, sims adding delays that aren't representative
• RL: TrackedFilmResponse work will be re-spun up in the next few weeks
  • If you want to try, please reach out and help break things to speed along development
• Caitlyn/Israel have paper/proceedings for LTD for silica phonon modeling 
  • Wondering where to put tools for computing density of states using phonopy – if self contained, put in tools directory
  • Will update confluence/readme with this paper
• Summer students:
  • Nolan/Wade at A&M on phonon 
  • Jack B. at A&M – e/h transport + IV scattering to compare with data and see if we need parameter tuning
  • Selby @ FNAL
  • BeEST at LLNL – some summer students to work on extracting material parameters
    • 1D RT modeling of QP tunneling in STJs
• John B:
  • How do I get started with G4CMP?
    • RL: start with geometries and work your way out from there
      • Also shoot messages to me on Slack
    • TC: Matthew Herndon at UW-Madison who can help with boilerplate Geant4
    • CSW: VIEWS tutorials available?
  • Studies of interest: shine red laser on back of device, measuring T1 dropout for qubits on a chip as a function of position of beam spot
    • After this, try thick aluminum on back
    • For short term MEMS studies:
      • Make geometry for your chip a la the strategies used in the RISQTutorial + present at G4CMP consortium meeting
      • Hop on call with Ryan/Selby about how to go about modeling the laser light
    • Skin depth in semiconductors at low temperatures – worried about laser hitting silicon
      • Mike: e/h pairs get created 5/10 μm below surface (current intuition)
      • Don't bother with the laser photon – just write primary generator to create e/h pairs at right depth profile is
      • Just do phonon burst at the various XYZ locations to start – if you care about further deviations, you can go further with e/h pair generation
• Anna H:
  • Working with John, reading through code
  • If G4 installation/build was made with OGL enabled, then vis will work. Otherwise it won't.
    • cmake option for this build: -DGeant4_USE_OPENGL_X11=ON
    • Other options/resources: https://geant4-userdoc.web.cern.ch/UsersGuides/InstallationGuide/BackupVersions/V10.7/html/installguide.html#geant4-build-options
      
      

Agenda:

• AOB

Attendees: Kelsey, Rik Bhattacharyya, B. Zatschler, Jared, Jesse, Mariano, Paul B., Samir, Siamak, S. Zatschler, Nolan, Warren, Tom Carroll, Emile, Chris S.

Announcements:

• Jared:  New paper on arXiv: 

  https://arxiv.org/abs/2505.04902, "The spatial correlation of radiation-induced errors in superconducting devices decays over a millimeter"

• G4CMP V09-07-00 just went out, including the phonon reflection improvements from today's talk.

Agenda:

• Phonon Specular Reflection on Curved Surfaces, Nolan Tenpas (A&M)
• AOB

Attendees: Siamak, Ryan, Jesse, Chris Moore, Chris Schnaible, Émile, Nolan, Matthew, Tom, Philip, Jared, Mike, Caitlyn

Announcements/Agenda/Discussion:

• Jared: put up instructions on style guide: how to use Clang tool. Copy of it is available for download and is currently in repo
• No RISQ this year, but another G4CMP tutorial in the works (part RISQTutorial and part TrackedFilmResponse) – if anyone has any suggestions for additional features/discussion, please let Ryan know
  • If LPS can do anything to help, keep them in the loop
• Nolan: significant progress on specular reflection displacement loop for phonons along curved surfaces.
  • Most of the physics tickets taken care of so far
  • Phonons reach side wall, enter displacement loop stepping along curved surface until their group velocity can point backward into bulk
    • Sims give 100% collection efficiency of those phonons – no errant losses into world volume
    • Wrote particleChange for phonons specifically to update volume assignment
  • Utilities: skip flats on detector surface (SCDMS-specific, want to know where lattice is relative to world space)
  • Expecting this to be out within a couple of weeks
• Émile: merged IV scattering into another branch, physics is done (branch 404), but unsure when going to put onto develop
  • Will put together big-picture slides for future meeting (next week)
  • Now is a first-principle derivation (based on FGR) rather than semi-empirical. Also has phonon emission! 
  • Conservation of energy/momentum+phonon emission to make sure physics is correct from bottom up
• Tom: G4CMP history lesson question:
  • Charge carrier trapping processes:
    • For trapping of charge carriers on neutral impurities, should there be a phonon emitted?
    • When the trap is deep, ~>1 meV potential, you want to emit an athermal phonon at the trapping point, compare energy of charge to depth of impurity and radiate off phonon
    • We cheated – in G4CMP, we assume shallow traps, so no radiated phonon
  • Impact ionization/trap ionization: in literature, Mike has found that these are different things
    • "Impact" ionization: high enough E-field for mobile charges in conduction band to gain enough KE to promote other valence band charges into conduction band ("charge-to-charge" impact)
      • Not modeled in G4CMP currently
    • "Trap" ionization: charged/neutral traps separate from the valence band, and presumably over time there is a population of these that can get knocked out
      • Seems like the freed charge carrier gets 1 meV by default – done for ease of coding. Have to give liberated charge some energy, which is meant to avoid G4 stopping/killing it
      • Gonna throw trap ionization into branch 404 – maybe we should reduce the energy dumped into the charge
        • Can we get a link to where this meV is found? Tom to-do
      • Flat background between peaks in measured NTL spectra consistent with this shallow trapping effect
        • Trap ionization gives excess above each e- peak
        • Charge trapping gives excess below each e- peak
    • Deep traps: would need to do bulk density of these, compute MFP from that, add distribution of trap depths, etc.
      • Looks a little different than existing trap ionization
• SiO2 materials from Caitlyn are now on production branch
• Jesse: are we actively implementing alloys?
  • SiGe alloys? 
  • Plan would be to pick a percentage and then do same work that Caitlyn has done for Silica
  • Mike: for continua, would like tool to be able to parametrically spit out config.txt file for that alloy
    • Make standalone utility program to do it for you
• Ryan: interesting use of G4CMP for TLS studies in qubits: https://journals.aps.org/prxquantum/pdf/10.1103/PRXQuantum.4.020356

Attendees: Ryan, Jake, Siamak, Caitlyn, Brenden, Matthew, Tom, Israel, Jared, Émile, Mariano Cababie, Samir Banik (HEPHY, in Vienna), Mike, Charles, Kiichi Okubo

Announcements: No announcements today

Agenda:

• General Q&A ("Office hours")
• Siamak: what are ML-related + modeling topics overlap
• Jared: CLANG format file to help with coding rules! (Personal use)
  • Would not recommend using with CLANG format, but would recommend using with IDE on blocks of code
  • Use with caution at the beginning
  • Don't do mass reformat of the package
  • Will try to get up early next week
• Jake:
  • Photon interactions in the code!
    • Scintillation in sapphire
    • Mike: Normal scintillation taken care of by Geant4 natively, but e/h recombination will be necessary to implement ourselves
• Émile: bottom-up intervalley scattering improved
  • First stab at G4-11
• Nolan: phonon reflection at curved surfaces – handling this in 
• Ryan: small updates on trackedFilmResponse, with visualizations:
  

  Tracked film response with very complex transmission line + qubit+resonator geometries, showing only QP
  Tracked film response with marginally complex transmission line geometry, showing phonons in green (some of which escape into thermal sink)
  Zoom-in showing diffusion across pad-transmission line joint.

   
• Caitlyn: created new feature branch with the SiO2 on it
  • Will soon make pull request!
  • Will reach out to Ryan about boundary interactions when she's ready to re-jumpstart that work
• Tom Carroll:  Could we replace G4CMPStackingAction with G4PrimaryTransformer?
  • G4CMP must have action to take new primary tracks and attach all the necessary auxiliary information.
  • Can't have multiple StackingActions; users with their own have to either call through or inherit from required G4CMP version.
  • Kelsey: G4PrimaryTransformer in 10.7.4 does not have any hooks available for subclassing: all of the actual working functions are non-virtual, so cannot be overloaded.
  • Will maybe investigate how to register StackingAction automatically, in G4CMPPhysics::ConstructProcess() maybe?  Find a way to respect user versions?

Attendees: Joe Fowler, Mike Kelsey, Ryan, Siamak, Brenden, Jesse Lutz, Ramya Suresh, Doug Pinckney, Paul Baity, Jeffrey Glasier, Stefan Zatschler, Jared Yamaoka, Matthew Natale, Anna Huynh, Nolan Tenpas, Tom Carroll, Philip Mason, Birgit Zatschler, Chris Schnaible, Eric Mascot, Gianpaolo Carosi, Nathan Nakamura

Announcements:

• New folks: Joe Fowler (NIST), Nathan Nakamura (NIST), Doug Pinckney (MIT), Ramya Suresh (Purdue)

Agenda:

• Introductions and quick APS recap
• "Energy Deposition in Superconducting Quantum Devices from Different Cosmic-Ray Components" - B. Longfellow (slides)
• Single-image update from TrackedFilmResponse - R. Linehan
• Time for other technical questions: 20-30 minutes

• AOB