Academic Appointments


  • Professor, Physics
  • Professor, Particle Physics and Astrophysics

Honors & Awards


  • Early Career Award, NSF (2011)
  • Alfred P. Sloan Fellowship, Sloan Foundation (2009)

Professional Education


  • Ph.D., UC Berkeley, Astrophysics (2003)
  • B.Sc., National Taiwan University, Physics (1994)

Current Research and Scholarly Interests


1. Searching/measuring primordial gravitational waves in the CMB (Cosmic Microwave Background) through experiments at the South Pole (BICEP and SPT), high plateaus in Tibet (AliCPT) and Atacama (Simons Observatory), as well as in space (LiteBIRD).

2. Development and applications of superconducting detector and readout systems in astrophysics, cosmology, and other areas.

2019-20 Courses


Stanford Advisees


All Publications


  • Constraints on Primordial Gravitational Waves Using Planck, WMAP, and New BICEP2/Keck Observations through the 2015 Season PHYSICAL REVIEW LETTERS Ade, P. R., Ahmed, Z., Aikin, R. W., Alexander, K. D., Barkats, D., Benton, S. J., Bischoff, C. A., Bock, J. J., Bowens-Rubin, R., Brevik, J. A., Buder, I., Bullock, E., Buza, V., Connors, J., Cornelison, J., Crill, B. P., Crumrine, M., Dierickx, M., Duband, L., Dvorkin, C., Filippini, J. P., Fliescher, S., Grayson, J., Hall, G., Halpern, M., Harrison, S., Hildebrandt, S. R., Hilton, G. C., Hui, H., Irwin, K. D., Kang, J., Karkare, K. S., Karpel, E., Kaufman, J. P., Keating, B. G., Kefeli, S., Kernasovskiy, S. A., Kovac, J. M., Kuo, C. L., Larsen, N. A., Lau, K., Leitch, E. M., Lueker, M., Megerian, K. G., Moncelsi, L., Namikawa, T., Netterfield, C. B., Nguyen, H. T., O'Brient, R., Ogburn, R. W., Palladino, S., Pryke, C., Racine, B., Richter, S., Schillaci, A., Schwarz, R., Sheehy, C. D., Soliman, A., St Germaine, T., Staniszewski, Z. K., Steinbach, B., Sudiwala, R. V., Teply, G. P., Thompson, K. L., Tolan, J. E., Tucker, C., Turner, A. D., Umilta, C., Vieregg, A. G., Wandui, A., Weber, A. C., Wiebe, D. V., Willmert, J., Wong, C. L., Wu, W. K., Yang, H., Yoon, K. W., Zhang, C., Keck Array Collaboration, BICEP2 Collaboration 2018; 121 (22)
  • Highly-multiplexed microwave SQUID readout using the SLAC Microresonator Radio Frequency (SMuRF) Electronics for Future CMB and Sub-millimeter Surveys Henderson, S. W., Ahmed, Z., Austermann, J., Becker, D., Bennett, D. A., Brown, D., Chaudhuri, S., Cho, H., D'Ewart, J. M., Dober, B., Duff, S. M., Dusatko, J. E., Fatigoni, S., Frisch, J. C., Gard, J. D., Halpern, M., Hilton, G. C., Hubmayr, J., Irwin, K. D., Karpel, E. D., Kernasovskiy, S. S., Kuenstner, S. E., Kuo, C., Li, D., Mates, J. B., Reintsema, C. D., Smith, S. R., Ullom, J., Vale, L. R., Van Winkle, D. D., Vissers, M., Yu, C., Zmuidzinas, J., Gao SPIE-INT SOC OPTICAL ENGINEERING. 2018

    View details for DOI 10.1117/12.2314435

    View details for Web of Science ID 000451719300023

  • BICEP2 / Keck Array IX: New bounds on anisotropies of CMB polarization rotation and implications for axionlike particles and primordial magnetic fields PHYSICAL REVIEW D Ade, P. R., Ahmed, Z., Aikin, R. W., Alexander, K. D., Barkats, D., Benton, S. J., Bischoff, C. A., Bock, J. J., Bowens-Rubin, R., Brevik, J. A., Buder, I., Bullock, E., Buza, V., Connors, J., Crill, B. P., Duband, L., Dvorkin, C., Filippini, J. P., Fliescher, S., Germaine, T., Ghosh, T., Grayson, J., Harrison, S., Hildebrandt, S. R., Hilton, G. C., Hui, H., Irwin, K. D., Kang, J., Karkare, K. S., Karpel, E., Kaufman, J. P., Keating, B. G., Kefeli, S., Kernasovskiy, S. A., Kovac, J. M., Kuo, C. L., Larson, N., Leitch, E. M., Megerian, K. G., Moncelsi, L., Namikawa, T., Netterfield, C. B., Nguyen, H. T., O'Brient, R., Ogburn, R. W., Pryke, C., Richter, S., Schillaci, A., Schwarz, R., Sheehy, C. D., Staniszewski, Z. K., Steinbach, B., Sudiwala, R. V., Teply, G. P., Thompson, K. L., Tolan, J. E., Tucker, C., Turner, A. D., Vieregg, A. G., Weber, A. C., Wiebe, D. V., Willmert, J., Wong, C. L., Wu, W. K., Yoon, K. W. 2017; 96 (10)
  • BICEP2/KECK ARRAY VIII: MEASUREMENT OF GRAVITATIONAL LENSING FROM LARGE-SCALE B-MODE POLARIZATION ASTROPHYSICAL JOURNAL Ade, P. A., Ahmed, Z., Aikin, R. W., Alexander, K. D., Barkats, D., Benton, S. J., BISCHOFF, C. A., Bock, J. J., Bowens-Rubin, R., Brevik, J. A., Buder, I., Bullock, E., Buza, V., Connors, J., Crill, B. P., Duband, L., Dyorkin, C., Filippini, J. P., Fliescher, S., GRAYSON, J., Halpern, M., Harrison, S., Hildebrandt, S. R., Hilton, G. C., Hui, H., Irwin, K. D., Kang, J., Karkare, K. S., Karpel, E., Kaufman, J. P., Keating, B. G., Kefeli, S., Kernasoyskiy, S. A., Kovac, J. M., Kuo, C. L., Leitch, E. M., Lueker, M., Megerian, K. G., Namikawa, T., Netterfield, C. B., Nguyen, H. T., O'Brient, R., Ogburn, R. W., Orlando, A., Pryke, C., Richter, S., Schwarz, R., Sheehy, C. D., Staniszewski, Z. K., Steinbach, B., Sudiwala, R. V., Teply, G. P., Thompson, K. L., Tolan, J. E., Tucker, C., Turner, A. D., Vieregg, A. G., Weber, A. C., Wiebe, D. V., WILLMERT, J., Wong, C. L., Wu, W. L., Yoon, K. W. 2016; 833 (2)
  • BICEP2/KECK ARRAY. VII. MATRIX BASED E/B SEPARATION APPLIED TO BICEP2 AND THE KECK ARRAY ASTROPHYSICAL JOURNAL Ade, P. A., Ahmed, Z., Aikin, R. W., Alexander, K. D., Barkats, D., Benton, S. J., BISCHOFF, C. A., Bock, J. J., Bowens-Rubin, R., Brevik, J. A., Buder, I., Bullock, E., Buza, V., Connors, J., Crill, B. P., Duband, L., Dvorkin, C., Filippini, J. P., Fliescher, S., GRAYSON, J., Halpern, M., Harrison, S., Hildebrandt, S. R., Hilton, G. C., Hui, H., Irwin, K. D., Kang, J., Karkare, K. S., Karpel, E., Kaufman, J. P., Keating, B. G., Kefeli, S., Kernasovskiy, S. A., Kovac, J. M., Kuo, C. L., Leitch, E. M., Lueker, M., Megerian, K. G., Namikawa, T., Netterfield, C. B., Nguyen, H. T., O'Brient, R., Ogburn, R. W., Orlando, A., Pryke, C., Richter, S., Schwarz, R., Sheehy, C. D., Staniszewski, Z. K., Steinbach, B., Sudiwala, R. V., Teply, G. P., Thompson, K. L., Tolan, J. E., Tucker, C., Turner, A. D., Vieregg, A. G., Weber, A. C., Wiebe, D. V., WILLMERT, J., Wong, C. L., Wu, W. L., Yoon, K. W. 2016; 825 (1)
  • Joint Analysis of BICEP2/Keck Array and Planck Data PHYSICAL REVIEW LETTERS Ade, P. A., Aghanim, N., Ahmed, Z., Aikin, R. W., Alexander, K. D., Arnaud, M., Aumont, J., Baccigalupi, C., Banday, A. J., Barkats, D., Barreiro, R. B., Bartlett, J. G., Bartolo, N., Battaner, E., Benabed, K., Benoit, A., Benoit-Levy, A., Benton, S. J., Bernard, J., Bersanelli, M., Bielewicz, P., BISCHOFF, C. A., Bock, J. J., Bonaldi, A., Bonavera, L., Bond, J. R., Borrill, J., Bouchet, F. R., Boulanger, F., Brevik, J. A., Bucher, M., Buder, I., Bullock, E., Burigana, C., Butler, R. C., Buza, V., Calabrese, E., Cardoso, J., Catalano, A., Challinor, A., Chary, R., Chiang, H. C., Christensen, P. R., Colombo, L. P., Combet, C., Connors, J., Couchot, F., Coulais, A., Crill, B. P., Curto, A., Cuttaia, F., Danese, L., Davies, R. D., Davis, R. J., de Bernardis, P., De Rosa, A., De Zotti, G., Delabrouille, J., Delouis, J., Desert, F., Dickinson, C., Diego, J. M., Dole, H., Donzelli, S., Dore, O., Douspis, M., Dowell, C. D., Duband, L., Ducout, A., Dunkley, J., Dupac, X., Dvorkin, C., Efstathiou, G., Elsner, F., Ensslin, T. A., Eriksen, H. K., Falgarone, E., Filippini, J. P., Finelli, F., Fliescher, S., Forni, O., Frailis, M., Fraisse, A. A., Franceschi, E., Frejsel, A., Galeotta, S., Galli, S., Ganga, K., Ghosh, T., Giard, M., Gjerlow, E., Golwala, S. R., Gonzalez-Nuevo, J., Gorski, K. M., Gratton, S., Gregorio, A., Gruppuso, A., Gudmundsson, J. E., Halpern, M., Hansen, F. K., Hanson, D., Harrison, D. L., Hasselfield, M., Helou, G., Henrot-Versille, S., Herranz, D., Hildebrandt, S. R., Hilton, G. C., Hivon, E., Hobson, M., Holmes, W. A., Hovest, W., Hristov, V. V., Huffenberger, K. M., Hui, H., Hurier, G., Irwin, K. D., Jaffe, A. H., JAFFE, T. R., Jewell, J., Jones, W. C., Juvela, M., Karakci, A., Karkare, K. S., Kaufman, J. P., Keating, B. G., Kefeli, S., Keihanen, E., Kernasovskiy, S. A., Keskitalo, R., Kisner, T. S., Kneissl, R., Knoche, J., Knox, L., Kovac, J. M., Krachmalnicoff, N., Kunz, M., Kuo, C. L., Kurki-Suonio, H., Lagache, G., Lahteenmaki, A., Lamarre, J., Lasenby, A., Lattanzi, M., Lawrence, C. R., Leitch, E. M., Leonardi, R., Levrier, F., Lewis, A., Liguori, M., Lilje, P. B., Linden-Vornle, M., Lopez-Caniego, M., LUBIN, P. M., Lueker, M., Macias-Perez, J. F., Maffei, B., Maino, D., Mandolesi, N., MANGILLI, A., Maris, M., Martin, P. G., Martinez-Gonzalez, E., Masi, S., Mason, P., Matarrese, S., Megerian, K. G., Meinhold, P. R., Melchiorri, A., Mendes, L., Mennella, A., Migliaccio, M., Mitra, S., Miville-Deschenes, M., Moneti, A., Montier, L., Morgante, G., Mortlock, D., Moss, A., Munshi, D., Murphy, J. A., Naselsky, P., Nati, F., Natoli, P., Netterfield, C. B., Nguyen, H. T., Norgaard-Nielsen, H. U., Noviello, F., Novikov, D., Novikov, I., O'Brient, R., Ogburn, R. W., Orlando, A., Pagano, L., Pajot, F., Paladini, R., Paoletti, D., Partridge, B., Pasian, F., Patanchon, G., Pearson, T. J., Perdereau, O., Perotto, L., Pettorino, V., Piacentini, F., Piat, M., Pietrobon, D., Plaszczynski, S., Pointecouteau, E., Polenta, G., Ponthieu, N., Pratt, G. W., Prunet, S., Pryke, C., Puget, J., Rachen, J. P., Reach, W. T., Rebolo, R., Reinecke, M., Remazeilles, M., Renault, C., Renzi, A., Richter, S., Ristorcelli, I., Rocha, G., Rossetti, M., ROUDIER, G., Rowan-Robinson, M., Rubino-Martin, J. A., Rusholme, B., Sandri, M., Santos, D., SAVELAINEN, M., Savini, G., Schwarz, R., Scott, D., Seiffert, M. D., Sheehy, C. D., SPENCER, L. D., Staniszewski, Z. K., Stolyarov, V., Sudiwala, R., Sunyaev, R., Sutton, D., Suur-Uski, A., Sygnet, J., Tauber, J. A., Teply, G. P., Terenzi, L., Thompson, K. L., Toffolatti, L., Tolan, J. E., Tomasi, M., Tristram, M., Tucci, M., Turner, A. D., Valenziano, L., Valiviita, J., Van Tent, B., Vibert, L., Vielva, P., Vieregg, A. G., Villa, F., Wade, L. A., Wandelt, B. D., Watson, R., Weber, A. C., Wehus, I. K., White, M., White, S. D., WILLMERT, J., Wong, C. L., Yoon, K. W., Yvon, D., Zacchei, A., Zonca, A. 2015; 114 (10)

    Abstract

    We report the results of a joint analysis of data from BICEP2/Keck Array and Planck. BICEP2 and Keck Array have observed the same approximately 400  deg^{2} patch of sky centered on RA 0 h, Dec. -57.5°. The combined maps reach a depth of 57 nK deg in Stokes Q and U in a band centered at 150 GHz. Planck has observed the full sky in polarization at seven frequencies from 30 to 353 GHz, but much less deeply in any given region (1.2  μK deg in Q and U at 143 GHz). We detect 150×353 cross-correlation in B modes at high significance. We fit the single- and cross-frequency power spectra at frequencies ≥150  GHz to a lensed-ΛCDM model that includes dust and a possible contribution from inflationary gravitational waves (as parametrized by the tensor-to-scalar ratio r), using a prior on the frequency spectral behavior of polarized dust emission from previous Planck analysis of other regions of the sky. We find strong evidence for dust and no statistically significant evidence for tensor modes. We probe various model variations and extensions, including adding a synchrotron component in combination with lower frequency data, and find that these make little difference to the r constraint. Finally, we present an alternative analysis which is similar to a map-based cleaning of the dust contribution, and show that this gives similar constraints. The final result is expressed as a likelihood curve for r, and yields an upper limit r_{0.05}<0.12 at 95% confidence. Marginalizing over dust and r, lensing B modes are detected at 7.0σ significance.

    View details for DOI 10.1103/PhysRevLett.114.101301

    View details for Web of Science ID 000350624500002

    View details for PubMedID 25815919

  • Detection of B-Mode Polarization at Degree Angular Scales by BICEP2. Physical review letters Ade, P. A., Aikin, R. W., Barkats, D., Benton, S. J., BISCHOFF, C. A., Bock, J. J., Brevik, J. A., Buder, I., Bullock, E., Dowell, C. D., Duband, L., Filippini, J. P., Fliescher, S., Golwala, S. R., Halpern, M., Hasselfield, M., Hildebrandt, S. R., Hilton, G. C., Hristov, V. V., Irwin, K. D., Karkare, K. S., Kaufman, J. P., Keating, B. G., Kernasovskiy, S. A., Kovac, J. M., Kuo, C. L., Leitch, E. M., Lueker, M., Mason, P., Netterfield, C. B., Nguyen, H. T., O'Brient, R., Ogburn, R. W., Orlando, A., Pryke, C., Reintsema, C. D., Richter, S., Schwarz, R., Sheehy, C. D., Staniszewski, Z. K., Sudiwala, R. V., Teply, G. P., Tolan, J. E., Turner, A. D., Vieregg, A. G., Wong, C. L., Yoon, K. W. 2014; 112 (24): 241101-?

    Abstract

    We report results from the BICEP2 experiment, a cosmic microwave background (CMB) polarimeter specifically designed to search for the signal of inflationary gravitational waves in the B-mode power spectrum around ℓ∼80. The telescope comprised a 26 cm aperture all-cold refracting optical system equipped with a focal plane of 512 antenna coupled transition edge sensor 150 GHz bolometers each with temperature sensitivity of ≈300  μK(CMB)√s. BICEP2 observed from the South Pole for three seasons from 2010 to 2012. A low-foreground region of sky with an effective area of 380 square deg was observed to a depth of 87 nK deg in Stokes Q and U. In this paper we describe the observations, data reduction, maps, simulations, and results. We find an excess of B-mode power over the base lensed-ΛCDM expectation in the range 30 < ℓ < 150, inconsistent with the null hypothesis at a significance of >5σ. Through jackknife tests and simulations based on detailed calibration measurements we show that systematic contamination is much smaller than the observed excess. Cross correlating against WMAP 23 GHz maps we find that Galactic synchrotron makes a negligible contribution to the observed signal. We also examine a number of available models of polarized dust emission and find that at their default parameter values they predict power ∼(5-10)× smaller than the observed excess signal (with no significant cross-correlation with our maps). However, these models are not sufficiently constrained by external public data to exclude the possibility of dust emission bright enough to explain the entire excess signal. Cross correlating BICEP2 against 100 GHz maps from the BICEP1 experiment, the excess signal is confirmed with 3σ significance and its spectral index is found to be consistent with that of the CMB, disfavoring dust at 1.7σ. The observed B-mode power spectrum is well fit by a lensed-ΛCDM+tensor theoretical model with tensor-to-scalar ratio r = 0.20_(-0.05)(+0.07), with r = 0 disfavored at 7.0σ. Accounting for the contribution of foreground, dust will shift this value downward by an amount which will be better constrained with upcoming data sets.

    View details for PubMedID 24996078