The Space Optical Clocks Project:Development of optical lattice clocks for future applications in space

S. Schiller1, A. Görlitz1, A. Nevsky1, S. Alighanbari1, S. Vasilyev1, C. Abou-Jaoudeh1, G. Mura1, T. Franzen1, U. Sterr2, S. Falke2, Ch.

Lisdat2, E. Rasel3, A. Kulosa3, S. Bize4, J. Lodewyck4, G. M. Tino5, N. Poli5, M. Schioppo5, K. Bongs6, Y. Singh6, P. Gill7, G. Barwood7, Y. Ovchinnikov7, J. Stuhler8, W. Kaenders8, C. Braxmaier9, R. Holzwarth10, A. Donati11, S. Lecomte12, D. Calonico13, F. Levi13,

K. Kemmerle14, M. Plattner14, C. Jentsch9, S. Schilt16, T. Kippenberg17 and members of the SOC2 teams

EFTF 2012

Mission on the ISSModular breadboard development

• Operate a Sr lattice optical clock with 10-17 inaccuracy on the

ISS (incl. frequency comb)

• Goal I: test Einstein‘s prediction of the time dilation in the

graviational field of the Earth and of the Sun with 10 times

higher accuracy than in the ACES mission

• Goal II: perform relativistic geodesy, i.e. local determination of

Key points

Clock laserOpticalClock

Frequency comb

Est. total mass 310 kgEst. total power 300 W

(ACES: 270 kg, 450 W)

Payload overview Principle of optical latticeclock

Laser developments

• Goal II: perform relativistic geodesy, i.e. local determination of

the gravity potential, at equivalent level of 1 cm height within

ca. 1 day measurement time

• Space clock is compared with a network of optical and

microwave ground clocks using high-performance microwave

and laser links

• ESA candidate mission within the ELIPS programme, since

2005

• Pre-phase A study completed (2011), clock development

currently funded by EC-FP7

• Natural follow-on of the ACES mission

• Launch after 2018

comb

MicrowaveFrequency

Comparison

Unit

Microwavelink

Opticaltelescopes

OpticalFrequency

comparison unit

Data acquisition unit

Data link

Large atom number→ potential highstability

Several lasers, all frequency stabilized:

Strontium: 461 nm, 689 nm, 813 nm, 707 nm, 679 nm, 698 nm (clock transition)

Ytterbium: 399 nm, 759 nm, 1388 nm, 578 nm (clock transition)

Transportable Sr 698 nm clock laser Interference-filter stabilized clock laser

Laser developments

Frequency stabilizationsystem for 3 lasers

Complete Sr laser system

1E-14

698 nm Laser

NIST spherical cavity [Leibrand 2011]

NIST 26 cm Yb cavity [Jiang 2011]

• Configuration rigidly fixes the position of the cavity up to acceleration of 50 g (FEM simulation)

• Measured ∆ν/ν = 3×10-11/g for vertical and 4.3 ×10-10/g and 11.6 ×10-10/g for horizontal accelerations

• setup 40 cm × 30 cm × 20 cm

• weight 6 kg

• ULE cavity (length 120 mm,

Laser specifications

Sr

The Sr breadboard clockBreadboard apparatus

main planning choices:1. compact breadboard

for frequency production2. all lights fiber delivered

Transportable Strontium Sourcemain requirements:1. compact design2. reliability

Sr breadboard aspects

repumper(497nm)

resonant

photomultiplier(possible)Chamber configuration

rods are screwed

Beam configuration• Atomic flux ~ 3 × 1011 atoms/s

• 1st stage MOT: ~ 6 × 107 trapped atoms at 1 mK

• 2nd stage MOT: ~ 7 × 106 trapped atoms at 1.8 µK

• Lattice: 2 x 105 trapped atoms

Lattice trapping and spectroscopy

462 nm, 813 nm, 707, 679 nm laser are so far integrated with Sr clock breadboard0.01 0.1 1 10 100

1E-16

1E-15

NIST 26 cm Yb cavity [Jiang 2011]

mod

σy(τ

)

τ (s)

• ULE cavity (length 120 mm, diameter 60 mm)

• fused silica mirrors with thermal compensations rings

• finesse of 460 000

• fractional frequency instability < 1 × 10-15 for 0.1 s < t < 300 s

Yb

100 mm triple ULE cavity(low and medium finesse)

2. all lights fiber delivered3. custom flange holding MOT coils

and oven with 2D cooling

2. reliability3. low power consumption

blue (461nm) andred (689) MOT

fromZeeman

slower

(497nm)

optical lattice (813nm)

clock-probe (698nm)

resonantprobe

custom flangeDN150CF

radiator tofix MOT coils

compensation coils

rods are screwed on the custom flange

MOT coil

50 Gauss/cmwith 1.6 A

power dissipation of

20 W for each coil

no water cooling

• Volume of physics package: 210 liter(excluding electronics and readboard plate)

• Mass: 120 kg

• Power: 110 W (Sr oven: 15 W, magnets: ~40 W; electronics: 20 W)

• Total volume 1200 liter

• Lattice: 2 x 105 trapped atoms

Dichroic telescope for MOT Spectroscopy of 88Sr, (preliminary)

Transportable Yb clock

optical breadboard 120 cm x 90 cmno water cooling

is neededDimensions: 22 cm x 36 cm

• Complete Yb system on transportable optical table (1 m x 2 m); clock laser separate

• compact vacuum system; optimized for optical access and implementation of optical lattice• all laser systems diode or fiber based:

- blue laser diodes for precooling MOT (@ 399 nm) - frequency doubling of a diode-amplified fiber laser

in a PPLN waveguide for 2nd stage cooling MOT (556 nm)

- amplified diode laser laser for optical lattice (759 nm)

• 759 nm interference-filter ECDL is underdevelopment

• Interference-filter ECDL at 399 nm is operational

• 20 mW 556 nm for 2nd stage cooling

Yb laser system (partially integrated)Yb trapping in optical lattice• Setup for 1D lattice (achieved)or 2D lattice (planned)

„Green“ laser

(556 nm)

Spectroscopy beam

• Frequency-stable 1389 nm repumper laser

• 1 Hz clock laser linewidth

Measurement of the black-body shift Demonstration of Sr 3D MOT loaded from a dispenser + 2D MOT sourceGoal: operate the tubes at 300 K and 400 K;

New design for a vibration-insensitiveYb cavity, 30 cm long

Lifetime in lattice

Transfer efficiency from2nd stage MOT to lattice

Lattice laser

(759 nm)

(556 nm)

Main

chamber

Atomics package developments

Permanent-magnet Zeeman

slower

2nd generation Sr clock

breadboard design

Optics schematic of transport and magic lattices. - Optical delay paths aremechanically translated to position the waist of the magic lattice and clocklaser beams in either of the BBR measurement tubes. Atoms loaded into thetransport lattice are shuttled into and out of BBR tubes by controlling (withAOMs 1 and 2) a travelling wave component of the standing wave.

Schematic of vacuum chamber with twoblackbody tubes. Right: blackbody tube with

external heater

Goal: operate the tubes at 300 K and 400 K;determine shift to equiv. Inaccuracy of 2 x 10-17

Loading of Yb MOTwithout Zeeman slower

With/without 2D MOT