Searching for Dark Matter Axions with ADMX-HF - …Searching for Dark Matter Axions with ADMX-HF...

Searching for Dark Matter Axions with ADMX-HF(The Axion Dark Matter eXperiment – High Frequency)

Ben BrubakerYale University

February 18, 2016

UCLA

Ben Brubaker (Yale) ADMX-HF UCLA Dark Matter 2016 1 / 26

Outline

Motivation and challenges for high-frequency haloscopes

Overview of ADMX-HF design

Progress towards quantum-limited noise performance

Status of first production data run

Near-term upgrade plans and R&D overview


Axion Parameter Space

Parameter spacemostly unexplored

ADMX-HF: bothpathfinder forhigh-mass regionand innovationtestbed

2 × KSVZ coveragefor 4 − 8 GHz(16 − 33 µeV) in 3years with currenttechnology


Haloscopes at High Frequencies

Challenges

At constant coupling,dνdt∼ ν−14/3

for resonator geometries used in axion searches to date

Largely due to small volume of high-frequency resonators

Standard Quantum Limit (SQL): kTS ≥ hν for linear amplifiers

Motivation

∼ 20 µeV axions provide closure density in simplest models

Cryogenics much simpler at 5 cm scale than 50 cm scale

Josephson parametric amplifiers (JPAs): tunable amplifiers in the2-12 GHz range which can approach quantum noise limitsBen Brubaker (Yale) ADMX-HF UCLA Dark Matter 2016 4 / 26

ADMX-HF Collaboration

Yale University (host)Steve Lamoreaux, Ling Zhong, Ben Brubaker, Sid Cahn

UC BerkeleyKarl Van Bibber, Maria Simanovskaia, Samantha Lewis,Jaben Root, Kelly Backes, Al Kenany

Lawrence Livermore National LabGianpaolo Carosi, Tim Shokair

CU Boulder/JILAKonrad Lehnert, Maxime Malnou, Dan Palken


ADMX-HF Design

9 T superconducting solenoid fromCryomagnetics

VeriCold dilution refrigeratoroperated at T ∼ 120 mK

Copper cavity with Q ∼ 20,000,tunable from 3.5 to 5.85 GHz

JPA: noise near SQL, tunable from4.4 to 6.5 GHz

Sensitive to P ∼ 2.5 × 10−23 W(≈ 1 5 keV WIMP event/year!)


Cavity and Motion Control

Qc ∼ 20,000, tunablefrom 3.5 to 5.85 GHz

Tuning via rotation ofoff-axis Cu rod

Kevlar lines forcryogenic motioncontrol: no heat load at100 mK

Linear drives fordielectric fine tuningand antenna insertion


Josephson Parametric Amplifier

An LC circuit with nonlinear SQUIDinductance⇒ parametric gain with a strongpump tone near resonance.

Added noise is just thermal noise of the “idlermode” from opposite side of pump

Apply DC magnetic flux to tune from 4.4 to6.5 GHz with ∼ 20 dB gain

Bucking coil, Pb/Nb/Cryoperm shields, andpassive NbTi coils for ∼ 108 net reduction offield on JPA


Noise calibration principle

kTS = hν(

1ehν/kT − 1

+12

+ NA

)

Linear detection: ≥ 1/2 photon at the input of any linear amplifier,because quadrature amplitudes don’t commute with Hamiltonian.

The Standard Quantum Limit: A phase-insensitive linear amplifiermust add noise NA ≥ 1/2, because quadrature amplitudes don’tcommute with each other.

Measure NA using blackbody source at known temperature (theY-factor method) – includes JPA added noise, HEMT added noiseand loss before JPA.

Y =PHot

PCold=

GH [NH + NA (NH)]

GC [NC + NA (NC)]


Noise calibration results

Design goal:TS ≈ 1.5hν ≈ 400 mK

We measure NA ≈ 1.5⇒ TS ≈ 575 mK offresonance

Total noise increases toTS ≈ 4hν ≈ 1.1K onresonance

Off-resonance noise consistent with 20% thermal contribution,3 − 7 K HEMT noise, 1 − 2 dB loss before JPA

Temperature- and gain-dependence of resonant noise bumpimplicates thermal link to tuning rod


Timeline

4/2012 − 6/2014:Design/construction

7/2014 − 1/2016:Integration/commissioning:

I Eliminated vibrationallycoupled JPA gain fluctuations

I Eliminated JPA/cavityinterference

I Eliminated IF spikes in spectraI Added analog flux feedbackI Implemented blind injection of

synthetic axion signals

1/26/2016: Production data runstarted!


Status of First Data Run

All parameters at design specs except TS

3 full scans, 1 month each, with ∼ 70% live time

We will cover 5.7 − 5.8 GHz at 2.5 × KSVZ sensitivity


Preliminary Analysis

Noise is Gaussian out to at least 3 σ and at least 5.5 hours of averaging


Preliminary Analysis


What’s Next?

R&D for next-generation searches:I Boost Qc : thin-film

superconducting cavities (UCB)I Evade SQL: preparing cavities in

squeezed states (CU)I Avoid V suppression: photonic

band gap cavities (UBC)

JPA/cavity fabrication to extendfrequency range

Improve thermal link to rod: reduceTS by ∼ 500 mK

Transfer experiment to newBlueFors dil fridge: more stable,reduced vibrations⇒ colder


Thank you!

We gratefully acknowledge support from the National ScienceFoundation, the Heising-Simons Foundation,

and the Department of Energy.


Extra Slides


Hybrid Superconducting Cavity R&D

Superconducting cavities: high Q, but notin high B fields.

Need cavity to withstand high static fields,not high RF power as in acceleratorapplications.

Thin film type-II superconductors (NbTiN,NbN, MgB2): high (Bc2)‖, no vortexdissipation if field is parallel and d . ξ

With appropriate coatings on barrel andcopper endcaps, we can increase Q by ∼the aspect ratio of the cavity (∼ 6×).

Plasma deposition system installed andcoating prototypes at UCB.


Squeezed states for axion detection

JPAs can operate in a mode where theyamplify one signal quadrature andsqueeze the other: no SQL

If we align the squeezed quadrature ofone JPA with the amplified quadrature ofanother, no 1/2 photon from lineardetection either: kTS � hν!

Cavity must be overcoupled; squeezedstate injected in reflection. Works due tofinite axion coherence time ∼ 200 µs.

Eliminating loss before JPA is a challenge.

Work on a prototype squeezed-statereceiver is underway at CU, perhapsready as early as late 2016.


Photonic band gap cavities

Isolate a single mode using a defect in an open periodic lattice ofmetal and/or dielectric rods

Much higher volume at a given frequency than conventionalcylindrical cavity; well-defined TM010 mode

Challenge is making them tunable

HPC simulations of resonator designs and tolerances at UCB


Bolometric axion detection

Thermal noise from whole cavity band,but no standard quantum limit.

δPlin

δPbol∼

√Qc

Qaehν/kT > 1 above 10 GHz.*

Perhaps even at lower frequencies if we can improve Qc .

Mature detector technology in AMO (Rydberg atoms), quantumcomputing (cavity QED), CMB (Transition Edge Sensors).

*: S. K. Lamoreaux et al., Phys. Rev. D 88, 035020 (2013).


Haloscope Signal Power

P ∼ g2aγγ (ρa/ma) B2QcVCnm`

(Matrix element)2

Axion number density

Virtual photon number density

Resonant enhancement of axion-photon conversion

Effective volume occupied by cavity mode

Form factor Cnm` =(∫

dV Enm` · B)2/(V

∫dV E2

nm`

)⇒ best for low-order TM modes: L ∼ ν−1

P ∼ 2.5 × 10−23 W (≈ 1 5 keV WIMP event/year!)


Haloscope Noise

Thermal noise in cavity bandwidth kBT ∆νc ≈ 10−18 W.

The Dicke radiometer equation:

SNR =P

kTS

√t

∆νa

Noise temperature TS includes blackbody and amplifier noise.

Linear detection:Qa ≈ 50Qc ⇒ ∆νa � ∆νc .

RMS noise decreases as 1/√

t .


Microwave Layout

3 paths for injection intofridge: transmission,reflection, JPA pump.

Cryo microwave switch(Radiall) and terminator atstill plate for Y-factormeasurement.

Second-stage amplifier:LNF LNC4_8A: TN ≈ 4 K.


Microwave Layout

GaGe ADC: 14 bits, 2 GS memory, 25 MS/s sampling.VNA for cavity and JPA measurements.


DAQ procedure

Noise is mixed down to MHzand digitized at 25 MS/s fort ∼ 15 min.

In-situ computation andaveraging of power spectrawith 100 Hz resolution.

Step resonance by ∼ ∆νc/4and repeat O

(104

)times.

Data rate ∼ 20 GB/100 MHz(500 TB/100 MHz to save fulltime series data).


Cavity Tuning


JPA Tuning

-0.4 -0.3 -0.2 -0.1 0.0 0.1

4.5

5.0

5.5

6.0

6.5

JPA current HmAL

JPA

freq

uenc

yHGH

zL

In 5 T field (blue) and no field (red)


JPA Tuning


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