Center for Gravitational-wave Astrophysics

David ReitzeUniversity of Florida

Vision• A 3rd generation gravitational-wave detector is absolutely

essential for answering fundamental questions in physics and astronomy

• The Center for Gravitational-wave Astrophysics (CGA) will lead the R&D for a U.S. 3rd generation gravitational-wave detector

• The CGA will deliver multi-disciplinary frontier science: – Precision measurement beyond the Standard Quantum Limit– Gravitational-wave physics and astrophysics– Novel optical materials and devices

• The PFC funding model is perfectly suited for the CGA

04/19/23 2

Enabling frontier physics on many fronts

04/19/23 3

B. P. Abbott et al. 2010 Ap.J. 713 671 Abbott et al 2009 New J. Phys. 11 073032 Abadie et al 2011 submitted

quantitatively determine nuclear matter equation of state

Gravitational Waves

04/19/23 4

• Gravitational waves or ‘ripples’ in space-time are miniscule dynamic strains (DL/L < 10-21 ) which require extreme precision interferometry (DL) and very long arm lengths (L)

• Very strong yet indirect evidence: measurements of orbital decay of binary pulsar PSR1913+16 by Hulse and Taylor, and several additional similar systems

• Gravitational waves are unique probes of the most violent astrophysical events in the universe: black hole mergers, supernovae, Big Bang

GW-Detection schemes/detectors

04/19/23 5

f [log10 Hz]41-1-9-15-18 -6

Inflation Probe PulsarTiming LISA LIGO

• NANOGrav Collaboration

• Sources: Background fromMBH-binaries

• Reach critical sensitivity: 2015

-5

• LIGO, VIRGO, LCGT, GEO

• Sources: NS/BH mergersSupernovaePulsars...

• Reach critical sensitivity: 2015

• Sources: SMBH mergersEMRIsGalactic binaries

• Guaranteed signals• Largest SNR• Being re-scoped

• Polarization in-Wave Background• Source:

Density Fluctuations Gravitational Waves

• 2020+

Third generation gravitational-wave astrophysics

• DUNCAN TO PROVIDE

04/19/23 6

Why the time is right to fund the CGA now!

• The path from concepts and proof-of-principle experiments to an operational interferometer is 20 years long – Initial LIGO: first design study completed in 1983, construction proposal 1989,

construction completed 1999, design sensitivity science run Nov 2005-Sept 2007– Advanced LIGO: design study completed in 1998, construction proposal 2006,

planned first data 2015, design sensitivity ~2016, discovery ~2017

• Discovery will drive demand - worldwide call by astronomers and astrophysicists for higher SNR, more detections, better localization, broader frequency coverage, … as soon as the first gravitational wave is discovered!

• The path to a 3rd generation gravitational wave detector might look like…– design study 2015 at the earliest, construction proposal 2020+, first light ~2030,

design sensitivity ~2032

• But only if we get started now!– European funded roadmap for 3rd generation Einstein Telescope was just delivered,

see http://blogs.nature.com/news/2011/05/post_78.html

04/19/23 7

But wait!! Shouldn’t we wait for results from Advanced LIGO??

• We’ll surely learn important instrument science lessons from Advanced LIGO (not just discover gravitational waves!)– Advanced LIGO can make important new discoveries about the nature of

gravitational waves and their sources.– Must address high power handling, thermal noise…

• We are certain that a 3rd generation interferometer will need to use drastically different technologies in several areas. – Those technologies will need to be developed, no matter what.

• Some of the research programs we are proposing can be used in Advanced LIGO to improve sensitivity or as alternatives should there be a problem with Advanced LIGO– e.g., optical filter cavities, seismic arrays, low frequency suspensions.

• Note that there will plenty of time to incorporate any relevant technical lessons from aLIGO into the 3G interferometer design.

04/19/23 8

04/19/23

2015-2025: 2nd Generation Gravitational Wave Detectors

GEO HFGermany

Advanced VIRGOItaly

Advanced LIGOLouisiana, USA

Advanced LIGOWashington, USA

LCGTJapan

Advanced LIGOAustralia?

04/19/23

2011: Coordinated 3rd Generation Research Programs

04/19/23

2030+: 3rd Generation Gravitational Wave Detectors

Einstein TelescopeEurope

Quantum-enhancedPrecision Interferometry

• Heisenberg Uncertainty Principle– Imposes Interferometry

Standard Quantum Limit (SQL)– Not a strict limit for strain sensing

• Goals:– Demonstrate technology that can surpass the SQL for

O(100kg) test masses

• Techniques:– Mitigate thermal noise (Silicon & cryogenic)– Exploit quantum correlations

• Squeezed light sources• Interferometer topology

(filter cavity, speed-meter)

04/19/23 12

2

hpx

Nature 464, 697-703, 2010

Nano-Mechanicaloscillatorin ground state(Nature 2009)

Quantum mechanicswith atoms(Schrödinger 1926)

Quantum limitedInterferometryfor m=150kg(GCA)

CGA Major Activities and How They Fit Together

• DUNCAN TO PROVIDE

04/19/23 13

CGA Education and Outreach

• Pipeline of activities spanning middle school to graduate school– including all CGA sites and partners – including postdocs as mentors and active participants

• APS Physics Quest High School interns and teacher training, College interns and women speakers series graduate summer school in experimental physics

04/19/23 14

CGA: a geographically dispersed PFC• 7 Universities, 22 faculty investigators.• Dispersion == strength. No single institution could focus 22 faculty lines in

a single area.• LIGO and LSC participation has taught most CGA faculty how to

collaborate beyond campus walls.• Communication is essential and built in.

– biweekly telecons of each Major Activity (EVO, video, …)– monthly telecons of the entire CGA– twice yearly face-to-face meetings of CGA particpants– ad-hoc face-to-face meetings at the LSC meetings: “open to all” meetings to

advertise the CGA to the LIGO community• The Quiet Optical Test Facility -- a gathering place for experimenters. • Affiliates, visiting fellows, national and international partners play an

important role.• A number of workshops each year.

04/19/23 15

Change in PFC director• Dave Reitze to become the Executive Director of the LIGO

Laboratory– At Caltech this summer; will be on leave from UF and will remain

affiliated with PFC researchers• David Tanner to assume the role of CGA Director

– Distinguished Professor at UF– former Physics Department Chair, – Chair of the APS Division of Condensed Matter Physics 2006-2007– Associate director UF Microfabritech

• The CGA organizational structure will remain the same– UF will retain lead institution status; Campanelli will retain Associate

Directorship • The personnel and structure of the CGA are such that this change

will not have a major impact – We have a ‘deep bench’ --- both technical and management.

04/19/23 16

Why a Third Generation GW research needs a PFC now

• A PFC-type Center for Gravitational Astrophysics is essential to advance the field beyond Advanced LIGO

• Timely & forward-looking – must start now to achieve a working 3rd generation detector in 2030

• Aggressive– measurement precision beyond the standard quantum limit! – large-scale underground detector!

• Potential to lead to a major advance – the science case for a 3rd generation gravitational-wave observatory is

compelling– much technology to be developed.

• A mix of disciplines and talents – designing a 3rd generation gravitational-wave observatory requires

coordination among a broad spectrum of scientific disciplines

04/19/23 17

Back up slides

04/19/23 18

Why this group?• Some of us have been involved with LIGO • Faculty investigators working with but not consumed by aLIGO

• The Quiet Optical Test Facility

04/19/23 19

Management

• Exec Board: Budgets; internal reviews; recommends adding or phasing out projects; selects director from among participants.

• Director: Liaison with NSF/Universities; report submission; facilities; organizes meetings; identifies problems to EB.

• 3 year terms for all, staggered in case of EB.

04/19/23 20

Example 3G strain sensitivity

04/19/23 21

• XylophoneLF + HF detector

• 10x lower freq.

• 10x lower strain

• Sub-SQLsensitivity

Squeezed light source

• Quantum trade-off between phase and amplitude noise

• Strain sensing is only sensitive to one of them

• Can be generated in Optical Parametric Oscillator

• Technology at 1.6u not ready

04/19/23 22

Wigner functionsof squeezed states(Nature 387, 471 – 475, 1997)

Schematic representationof Electric field, various states

Squeezed light source

• Conceptual layout of squeezer

• Light is frequency-doubled in SHG

• Squeezed vacuum created in OPO

• Control loops for cavity and phase locking

04/19/23 23

Interferometer configurations

• Several layouts for sub-SQL interferometry have been proposed– None have been experimentally demonstrated– Technical challenges, sensitivity to real world losses, technical noise couplings, etc.

04/19/23 24

Two very different speed-meter configurations

DUSEL Status• Recent DUSEL developments have limited implications for the CGA

activities. • Homestake mine will continue to support scientific research over the

coming 2-3 years (and likely longer) through a combination of private and federal funding.

• This period will be sufficient to complete the measurements we planned for the Homestake mine.

• Further, our interest is not limited to the Homestake location:– We will conduct a systematic survey of (surface and

underground) locations across the US that could potentially host such a 3G detector.

• While Homestake appears promising, it remains to be seen whether the seismic noise levels and geological structure at Homestake are indeed optimal for a 3G gravitational-wave detector.

04/19/23 25

Seismic and Newtonian Noise

• Seismic and Newtonian (gravity-gradient) noise sources dominate below 10 Hz in surface detectors.

• Newtonian noise sources:– Seismic waves (dominated by

surface waves).– Atmospheric fluctuations.– Human factor (traffic etc).

• Newtonian (strain-equivalent) noise estimate: ~10-20 Hz-1/2 at 1 Hz.– Need to suppress it by 103–104x.

04/19/23 26

Mitigating Newtonian Noise

• Survey US locations in terms of seismic noise and atmospheric conditions.

• Underground option:– Controllable environment, atmospheric

and human-induced effects suppressed.

– Surface seismic waves exponentially suppressed with depth (10x at 1 Hz).

• Active suppression of seismic contribution:– Monitor the rock motion, feedback to

interferometer mirrors.– Need a large array of underground

seismic stations.– Testing the feasibility of this option at

the Homestake mine.

04/19/23 27

Average seismic levels at 1.1 HzUSArray seismometer data

Homestake Project

04/19/23 28

Current 8-element array of seismic stations at Homestake. Propose to expand the array to ~30 stations, with a full 3D configuration.

Seismic spectrum at 4100 ft depth. Homestake is remarkably quiet!

Underground vs Space

• Cost of boring multi-kilometer tunnels is certainly substantial.– Of order $100M-$300M, depending on length, geology etc.– For comparison, initial LIGO cost was $280M.

• Already being demonstrated by the LCGT project in Japan: L-shape interferometer, 3km arms.

• European design study for Einstein Telescope already completed, assumes underground environment: triangular shape, 10km sides.

• 3G detectors would be complementary to satellite-based interferometer, which will probe frequencies around 1 mHz.

• Cancellation of LISA leave the future of the US contribution to the satellite-based detectors rather uncertain.

• It is critical for the US to initiate a systematic and detailed design study for 3G gravitational wave detectors to maintain the leadership momentum and the competitive edge generated by LIGO.

04/19/23 29

LCGT

04/19/23 30

Large-scale Cryogenic Gravitational-wave Telescope

Kamioka, Japan3km arms, L-shapedObservations starting ~2017.

Einstein Telescope

04/19/23 31

Artist’s impression of Einstein Telescope

Marco Kraan, Nikhef, ET science team

Triangular,10 km arms,Cryogenic,6x detectors.

PFC research could contribute in an effective way

Paper design so farMuch enabling technology “to be”done

04/19/23 32

Low-Frequency Suspensions

FmNN

S

S

2 g2 m

2

Fg

Fm

Fg

• Pendulum suspension provides f-2 suppression of motion above resonant frequency.

• To operate at ~1 Hz, need resonant frequency ~0.1 Hz 25m long pendulum!

• Possible alternative: cancel the gravitational restoring force with magnetic or electrostatic forces, lowering the resonant frequency.

• Propose to investigate low-frequency pendulum designs.

33 George Hobbs, CSIRO

The Gravitational Wave Spectrum

CMBpolPlanck

Ground-based Interferometers

Advanced LIGO: 2015Advanced Virgo: 2015

Einstein Telescope: 2025 ?

Space-based InterferometersNGO: 2022 ?(formerly LISA)

Ground-based Radio Astronomy

NanoGrav: 2015SKA: 2020 ?