Michèle Heurs Max-Planck-Institut für Gravitationsphysik & QUEST -- Leibniz Universität Hannover

OIST Workshop Okinawa

May 2013

MPI für Gravitationsphysik Albert-Einstein-Institut

Hannover

May 2013 OIST Workshop Okinawa 3

non-classical light sources: squeezed light at high free spectral ranges

controls theory: modern control, coherent control, traditional control

electronics: high-frequency large bandwidth photodetection

precision metrology: stable high-finesse optical resonators, gravitational wave detection

Visit our new website!

http://quantumcontrol.aei.uni-hannover.de/

Gravitational Waves and the interferometric gravitational wave detector network

Standard Quantum Limit of interferometry

Radiation Pressure Noise

Coherent Quantum Noise Cancellation (CQNC)

Limitations to CQNC

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Interferometric GWDs are quite complex systems

„Free running“ they are not ready for measurement due to fluctuations (= noise)

→ GWD needs to be held in a very delicate state in many ways at all times (= controlled)!

What noise? And how to control?

GWs are quadrupole waves → effect on a ring of test masses:

GWs are very weak → 1 km baseline only changes by 1‰ of a proton diameter (10-18 m)

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laser

beam- splitter

mirror

mirror photodetector

constructive interference

destructive interference

nort

h ar

m

east arm

n·λ/4

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May 2013 9 OIST Workshop Okinawa

laser system

modecleaners

Michelson interferometer with dual recycling

and folded arms

May 2013 10 OIST Workshop Okinawa

Ultra-precise laser stabilisation (in frequency, intensity and geometry)

Lowest-loss substrates and coatings Multi-state pendulum suspensions for

optics Ultra-high vacuum system Recycling techniques / arm cavities Over 250, partly nested control loops

Squeezed light injection

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measures against technical noise

reduces shot noise, i.e. quantum noise

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Radiation Pressure Noise (RPN) is backaction noise

Shot Noise (SN) is detection noise

...both are caused by Poissonnian photon statistics

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More power reduces (relative) SN:

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More power increases RPN:

RPN is backaction noise → its effect looks like a GW...

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SQL

lower power

higher power

SN RPN

(Picture courtesy of S. Goßler)

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...will be limited by quantum noise above ~12 Hz (private communication with S. Hild)

higher mirror masses for RPN reduction → only possible to a certain degree...

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Best idea: eliminate RPN where it happens! But HOW? O.o Ponderomotive squeezing schemes

(H. J. Kimble et al., Phys. Rev. D, Vol. 65, 022002) Frequency-dependent squeezed input Variational output Squeezed variational

Or: what we’re doing!

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SQL

Low power

High power SN

RPN

SQL

SN RPN

x

Interferometer sensitivity (force measurement):

Mechanical oscillator (position measurement):

(Picture courtesy of S. Goßler)

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Scheme proposed by M.Tsang, PRL 105, 123601 (Sep. 2010): meter cavity field experiences backaction via opto- mechanically coupled mirror “anti-noise” from ancilla cavity field (through coupling via beamsplitter and χ(2) medium) causes destructive interference with RPN!

Theoretical schematic from M.Tsang, PRL 105, 123601 (Sep. 2010)

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May 2013 OIST Workshop Okinawa

• mechanical susceptibility:

ancilla cavity susceptibility:

Constraints for ideal CQNC:

22

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• Susceptibilities match to a certain power level

• Sensitivity off-resonance is increased by a factor of

with CQNC

without CQNC

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• Susceptibilities match to a certain power level

• Sensitivity off-resonance is increased by a factor of

with CQNC

without CQNC

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What if the susceptibilities do not match?

Can we really achieve perfect matching of χm(ω) and χa(ω)?

“Back of the envelope” estimation:

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As long as we’re sideband resolved and have a large Q we still get sensitivity enhancement off-resonance

Imperfect matching of coupling ratios and reduces effect further

Imperfect phasematching → later

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for (and plotted at )

ideal CQNC nCQNC “penalty”

SQL

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for (and plotted at )

ideal CQNC

matched coupling

SQL

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May 2013 OIST Workshop Okinawa 30

Jonathan Cripe (visiting student on DAAD stipend)

Timo Denker (PhD student)

Dirk Schütte (PhD student)

Daniel Steinmeyer (Master student)

Maximilian Wimmer (PhD student)

Klemens Hammerer (collaborator)

Mankei Tsang (collaborator)

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...and come visit our poster!