Atoms and Lasers for Precision Timing and PositionLeo Hollberg

National Institute of Standards and Technology (NIST) , Boulder CO

Astronomical

Sundial

Pendulum

Harrison

Atomic

Optical Frequency Measurements GroupNIST, Boulder

Optical ClocksChris OatesCold Ca Yann Le Coq → (SYRTE, Paris)Jason Stalnaker → (Oberlin)Guido Wilpers (Germany/NPL-UK)Anne Curtis (CU → NPL-UK)Kristin Beck (Rochester, SURF)Cold Yb Chad Hoyt (→ Bethel College)Zeb Barber (CU) Valeriey Yudin (Russia)Aleksei Taichanachev (Russia)Nathan Lemke (CU)Nicola Poli (LENS, Italy)

fs Frequency CombsScott Diddams

Tara Fortier (LANL)Jason Stalnaker → (Oberlin)

Qudsia Quraishi (CU)Stephanie Meyer (C)U)

Albrecht Bartels → (Konstance)L-S Ma, Z. Bi, (ECNU-BIPM)Y. Kobayashi (AIST Japan)Vela Mbele (South Africa)

Matt Kirchner (CU)Andy Weiner* (Purdue)

Danielle Braje

Optical Length MetrologyRichard Fox

•$$ NIST, DARPA-MTO, ONR-CU-MURI, NASA, LANL

Chip Scale Atomic Devicesclocks, magnetometers …

John KitchingSvenja Knappe (Germany)Peter Schwindt (Sandia)

Vishal Shah → (Princeton)Vladi Gerginov (Bulgaria)Ying-Ju Wang (Taiwan)

Clark GriffithAndy Geraci

Hugh RobinsonLiz Donley

Eleanor Hodby (England)Alan Brannon (CU)Brad Lindseth (CU)Matt Eardley (CU)

Susan SchimaLucas Willis (LSU, SURF)Nicolas VanMeter (SURF)

NIST Opto-ElectronicsNate Newbury, Bill Swan ...

Accuracy of clocks through historyAccuracy of clocks through history

Year (AD)

Chinese Hydro-mechanical

Verge & Foliot Balance

Huygens Pendulum

Free Pendulum

Barometric Compensation

Shortt

Quartz Crystal

Early Caesium Clocks

Primary Caesium Clocks

Reifler

Harrison’s Chronometer

Graham’s-Escapement

Cross Beat Escapement

1000 s / d

1000 1200 1400 1600 1800 2000

1s / d

1ms / d

1 µs / d

1ns / d

1ps / d

Temperature Compensation

Futu

re

1010-9-9

1010-3-3

1010-15-15

Fractional Error

Δt/t

Highest Accuracy Atomic Clocks

Current Microwave-Based Standards and Distribution

Approaching the limit for standards and distribution systems.

NISTMeasurementSystemHydrogen

Masersand

CesiumClocks

NIST-F1

GPS

Communicationssatellites

Radiobroadcasts

Δf/f ~ 1x10-15

for standardsand distribution

Rb and/or Cs

T. Parker et al.

Examples of Atomic Clocks for the Future Today ?

• Optical Atomic clocks – use lasers rather thanmicrowaves to probe atoms

• CSAC (Chip Scale Atomic Clocks) for hand held portablesystems

Optical Atomic frequency Standard

Cs

9,192,163,707 Hz

Laser coolingand detection

852 nm

Laser Coolingand detection(Blue or UV)

Optical ‘Clocktransition 1015 Hz

Microwave Atomic frequency Standard

Microwave clock transition

HeNe 633 nm

Frequency Lock electronics

!"

n

c=

I2

Michelson Interferometer,BIPM, Paris, circa 1910 ?

Relative position, dimensional metrology, surveying instruments relyon the fixed speed of light c and frequency references

discharge lamps, lasers and purely classical optics

Lunar ranging w/laser pulses

NIST F1, Cs atomic fountain clockPrimary frequency Std. of U.S.

S. Jefferts, L. Donley, T. Heavner, T. Parker

Δν

Ca

Detector

Local Oscillator

High-Q resonatorQuartz

Fabry Perot cavity

Feedback SystemLocks LO to

atomic resonance

Microwave SynthesizerLaser

456 986 240 494 158

Counter

υ

Generic Atomic Clock

Atoms

Advantages of Optical Clocks Quantum Projection Noise Fractional Frequency instability ~

! = observation time

N = number of atoms

5

10

15

0

010

10

10!!

microwave

optical

f

f

• Large number of atoms 106 or more• High signal/noise• Possibility of lattices

Candidate neutral atomsCa, Sr, Yb, Mg, H, Ag, Hg…

One atomic clock is always “perfect”Two similar clocks -- hard to detect systematic errorsDifferent types of clocks can determine most accurate and stable

Clocktransition

S

1P3P or D

Cooling/detectiontransition

y!"

"#

atoms

cycle

N

TK

0

$=

Δν

ν0 ν

Optical SynthesizerDivider / Counter

Cold Atom Optical Frequency Reference

µ-wave out

optical out

fr

0

I(f)

f

Ca Oven

fn = nfr

Stable opticalCavityLaser source

Optical Atomic Clocks

σ(τ

)

H-maser

Cs

Hg+

projected

Ca

1 day 1 month

Ca projected

Oscillator Stability

GPS

Optical Cavities

0.5 Hz @500 THZ

1 fs

Frac

tiona

l Fre

quen

cy U

ncer

tain

tyAccuracy of Atomic Frequency Standards - History

1.0E-18

1.0E-17

1.0E-16

1.0E-15

1.0E-14

1.0E-13

1.0E-12

1.0E-11

1.0E-10

1.0E-09

1970 1975 1980 1985 1990 1995 2000 2005 2010 2015Year

state-of-the-art Cs microwave

Ion

InfraredVisible

Alk. Earth

Cold Calcium optical atomic clock

Relative 657 nm Probe Detuning (MHz)

423 nm coolingΔν = 34 MHz

657 nm clock

1S0 (4s2) m=0

1P1 (4s4p)

Δν = 400 Hz

3P1 (4s4p) m=0

0

10

20

30

40

Perc

ent o

f Ato

ms E

xcite

d

0 2 4 6 8 10 12 0 1000 2000 3000 4000Relative Probe Frequency (Hz)

-0.2

-0.1

0.0

0.1

0.2

Dem

odul

ated

Sig

nal (

V)

60 seconds data acquisition 400 Hzlinewidth

423 nm MOT

5x106 atomsCa

-20 -15 -10 -5 0 5 10 15 200.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

Ato

m n

um

be

r [a

.u.]

Frequency offset [Hz]

Ytterbium optical atomic clock

Chad Hoyt Zeb BarberChris Oates

- Excellent prospects for high stability and small absolute uncertainty

398.9 nm,28 MHz

3P0: 578.42 nm,~15 mHzClock Transition

1P1 (6s6p)

3P1: 555.8nm, 182 kHz

3P0,1,2 (6s6p)

Lattice759 nm

full width ~ 4 Hz (Q >1014)

Candidates:

Sr, Yb, Ca, Hg

Stability of two optical freq. ref: Yb and Ca

1 10 1001E-16

1E-15

1E-14

0.1

1

Alla

n de

viat

ion σ y(τ

)

Averaging time (s)

Fre

quen

cy p

reci

sion

[Hz]

Δν

Ca

Detector

Local Oscillator

High-Q resonatorQuartz

Fabry Perot cavity

Feedback SystemLocks LO to

atomic resonance

Microwave SynthesizerLaser

456 986 240 494 158

Counter

υ

Generic Atomic Clock

Atoms

Enthusiasm for Optical Atomic Clocks and fs Combs

Jan Hall

Ted Hänsch

Nobel Prize2005

ScottDiddams

TaraFortier

20 fs

Ultrashort optical pulse, plus nonlinear fiber → Broad SpectumRepetitive pulse train → Frequency Comb → “ruler for frequency/time”

Count Optical Frequencies with Optical Frequency CombsUltra-short and repetitive pulses of light

time

Wavelength

Power

•Initial efforts/ideas: J. Eckstein, A. Ferguson & T. Hänsch (1978), V. P. Chebotayev (1988)

I(f)

f

fo

0fn = n frep + fo

frep

x2 f2n = 2nfrep + fo

fo

Self-Referenced Optical Frequency Sythesizer

Jones, et al. Science 288, 635 (2000)

Ideas, existed many places, Telle &Keller …, Udem, Hänsch …

Optical Freq. Ref

Ti:SapphireGain

convex

532 nmPump

Microwave out

The frequency of a mode is simply FN = N * frep – f0Where N is and integer ~ 10

6

Frequencyfr=1/ τr.t.

f0

frep ~ 1000 MHz

0

0

~5 x 105 Magnification

fs Pulse Train(Clock Output)

CW Laser Output500 THz

time

Diddams, et al.

1 ns

~2 fs

500 THz Optical Oscillator

Microwave Output~1 ns per tooth

Hg+

~1 fs per tooth Femtosecond Laser Comb

1,000,000:1 Reduction Gear(not to scale)

Mechanical Analogy of the Optical Clock

Counter &Display

Applications of Optical Frequency Ref. and Combs

•Advanced communication systems (security, autonomous synchronization)

•Advanced Navigation (position determination and control)

•Precise timing (moving into the fs range)

•Tests of fundamental physics (special and general relativity, time variation offundamental constants)

•Sensors (strain, gravity, length metrology ……)

•Ultrahigh speed data, multi-channel parallel broadcast, or receivers, coherent communications

•Low noise microwaves, and electronic timing signals

•Scientific applications ( precision spectroscopy, chemistry, trace gasdetection… )

•Quantum information ( Ivan Deutsch …)

•Fourier synthesized arbitrary waveform generation

fµ-wave= fopt/Nµ-wave out

Opticalreference

0

I(f)

ffµ-wave

fopt

PUMP

OCM3

M1 M2

fs frequency combs as Optical Frequency DividerGeneration of microwaves with low phase noise

1 ns

time

Optical outputs

30ps

Microwave pulses

20 fs

I(f)

fMicrowave frequency

Microwave comb w/1 GHz mode spacing

-160

-140

-120

-100

-80

-60

-40L(f

) dB

c/H

z

100

101

102

103

104

105

106

Frequency (Hz)

Low phase-noise microwaves, 10 GHz

Optical FrequencyDivider

State of the art sapphire oscillator

State of the art microwave synthesizer

Opt. Divider Data from Hollberg et al. proceeds IEEE MWP meeting Oct. 04

J. McFerran et al. Elect. Letter 2005

Hg+ optical cavityCavity kT

Photo detected shot-noise

atoms

Laser Source563 nm

linewidth ∆n <1Hz

Beat Frequency2(ƒAO + Δƒ + ƒN)

LO = 2ƒAO

Lock Δƒ = -ƒN

ƒ0

λ/4

PBS

Polarizer

AOM

ƒ0 + ƒAO + Δƒ

Angle-cutfiber facet

ƒAO + Δƒ

Polarization Control

λ/4

Fiber adds Noise ƒNDue to vibration, Δ

T…

ƒ0 + ƒAO + Δƒ + ƒN

Flat Fiber face

ƒ0 + ƒAO To Experment

Cancellation of Fiber Noise

Source Lab

ooo

Receiver Lab•For highest precision must useDoppler cancellation methodsto remove environmentalinduced phase shifts

Optical Frequencies Measured via GPSR. Fox, S. Diddams NIST,

also similar work at NPL …

I(f)

foptical

x2Self-Referencing

frep

funknown

GPS

Fox et al. Applied Optics, 05,

Even commercial systems nowavailable – CLEO/QELS trade show

Red, 633nm I2 – Stabilized HeNe laser

Advanced cold atom clocks orLaser ranging/imaging in/from Space

Next generation Gracelaser ranging ?

PARCS

NASA

ACES

ESA

HYPER, …

T2L2ESA

CSADs TeamNIST Time and FrequencyJohn Kitching Svenja Knappe Vladislav Gerginov Vishal Shah Susan Schima Peter Schwindt Clark Griffith Brad Lindseth

Ying-Ju Wang Matt Eardley

Elizabeth Donley Eleanor Hodby Hugh G. Robinson

NIST Electromagnetics John Moreland Li-Anne Liew

University of ColoradoZ. PopovićA. BrannonJ. BreitbarthJ. MaclennanY. Li

CSAC

CSAM

Gyro

Dir. Coup.

MEMS

LO

Wall coatings

Chip Scale Atomic DevicesCSAC (clock), CSAM (magnetometer), CSAG (gyro)

Optical excitation, atoms, MEMS, VCSEL lasers, low powerBattery powered devices, connect to application requirements

Cell Fabrication: Anodic Bonding• Preform created by KOH etching or

DRIE of Si

• Pyrex bonded on one side withanodic bonding

• Cell preform filled with Cs– BaN6 + CsCl → BaCl + Cs + 3N2

@ 150 ºC

• Diced cells made at NIST using theanodic bonding technique– Interior: 1 mm x ∅ 0.9 mm– Exterior: 1.33 mm x (1.45 mm)2

Pyrex 7740 (125 µm)Silicon (375 µm)Pyrex 7740 (200 µm)

L. Liew, et al., Appl. Phys. Lett., 84, 2694, 2004.

1 mm1 mm

NIST Chip-Scale Atomic Clock: 2004

Volume:9.5 mm3

Cell volume:0.81 mm3

Cell temp:85 ºC

Heatingpower:75 mW

Stability:σy(1 sec.) =2.5×10-10

S. Knappe, et al., Appl. Phys. Lett. 85, 1460 (2004).

1 mm

4.2 mm

1.5 mm

CSAC Frequency StabilityShort-term stability: 4×10-11 @ 1 sec

S. Knappe, et al., Opt. Express 13, 1249-1253 (2005).

Longer-term stability: 1×10-11 @ 1 hr

S. Knappe, et al. Opt. Lett. 30, 2351-2353(2005).

20000 30000 40000 50000

-4

-2

0

2

4

Rela

tive F

requency

(10-9

)

Time (sec)

1 mm

100

101

102

103

104

105

10-12

10-11

10-10

10-9

1 day1 hour

Alle

n D

evia

tion, !f/f

" (sec)

87Rb

DriftCs CSAC: -2 x 10-8/day87Rb Cell: <<1 x 10-10/day

(A Very Rough) Oscillator Comparison

Adapted from figure by R. Lutwak, Symmetricom

Quartz CrystalOscillators

Applications of Microfabricated Atomic Clocks

• Size (1 cm3)• Power (30 mW)• Precise timing: higher-performance, more reliable operation

Integration in portable, battery-operated devices

Key application areas:• Global positioning and navigation (GPS)

• Faster acquisition time• More precise altitude determination• Direct P(Y)/M code acquisition → anti-jam capability• Position solution with < 4 satellites visible

• Wireless communications, network synchronization• Fewer dropped cell phone calls• Avoidance of data accumulation

• Data logging, seismology, remote sensors…• Others we don’t even know about

GPS Positioning with < 4Satellites

τ1τ2

τ3

τ4

Atomic clock

?

(τ1, τ2, τ3, τ4)

(x, y, z, t)GPSReceiver

Commercialization of Chip-Scale Atomic ClocksHoneywell

(courtesy D. Youngner)Symmetricom/Draper/Sandia

(courtesy R. Lutwak)

RF output

Complete functioning CSACs

< 10 mWpower requirement

10 cm3

108 mW5×10-11 @ 100 s

1.7 cm3

57 mW4×10-12 @ 1 hr

bench wafer

Photo -detector

vcsel

Trans -Impedance Amp

optics

bench wafer

Photo -detector

vcsel

Trans -Impedance Amp

bench wafer

Photo -detector

vcsel

Trans -Impedance Amp

bench wafer

Photo -detector

vcsel

Trans -Impedance Amp

optics

top cap wafervacuum

gold reflectortitanium getter

soldersolder

top cap wafervacuum

gold reflectortitanium getter

soldersolder

optical pathoptical path

cavity wafer

rubidium +AR/N2

cavity wafercavity wafer

rubidium +AR/N2

Magnetometry with Chip-Scale Devices

Ato

m E

nerg

y

mFj

-2 -1 0 +1 +2

Hyperfinesplitting

Zeeman splitting

ћωHF

ћωL = ½µΒΒ

MX Magnetometer

Vaporcell

SemiconductorLaser

Photodetector

B

RFCoils

λ/4Filter

Optical

Microwave νhf

Ene

rgy

D1

A. Bloom, E. Alexandrov, A. Weis, and many others

• Improved sensitivity; no GHz oscillator

ΔB

CSAM Operation

2 kHz Sidebands

Width = 1.7 kHz or 243 nT

Heater Currents

Laser Current

Local OscillatorDriving RF Coils

Lock-in Amplifier

Photo-DiodeSignal

Data Acquisition

LoopFilter

MX CSAM Performance

Sensitivity Frequency Response

F3dB = 1 kHz

Magnetocardiography with a CSAM• At U. Pittsburgh with Dr. V. Shusterman• Mouse anaesthetized, placed near CSAM• ECG and MCG signals recorded

4.5

mm

1.7 mm12

3

6

4

(a) (b)

5

4.5

mm

1.7 mm12

3

6

4

(a) (b)

5

CSAM Sensitivity Comparison

Geo-physical Transient

Electromagnetics

Magnetic AnomalyDetection

Magnetocardiography

Magneto-encephalography

SQUID Susceptometry

Non-Destructive Test and Evaluation2004

2005

2006

High Tc SQUID

Low Tc SQUID87Rb, 1 mm3 atom shot noise

Adapted from R. L. Fagaly, Rev. Sci. Instrum., 77 (2006).

Nuclear Spin Gyroscopes• Much work in 1970s and 1980s

– Fraser (1963), Bayley, Greenwood, Simpson (1973)– Commercial development: Litton, Singer-Kearfott, TI

Alkaliatom

Noble gasatom

B0

ΔB1 ΔB2Mng

MAlPD

SpinExchange

Time

100 µs

58 ms 0

1

N RB! +"

0

1

NB!

ΩR

FFT of Lock-In Signal

! = 100 us, S=200 mV

f (Hz)

0 5 10 15 20 25

PS

D (V

rms/rtH

z)

1e-6

1e-5

1e-4

1e-3

1e-2

1e-1

Lock In signal Fit includes linear drift

f=y0+c*x+a*exp(-x/d)*cos(2*3.14159265359*x/b)

t (s)

0 5 10 15 20

S (V

)

-0.8

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

T2 ~ 6 s

129Xe

OPTICS + atoms/molecules new capabilities• Cold atoms, stable lasers and femotosecond optical frequency combs

having tremendous impact on fundamental science, precision measurements,and metrology

• Optical/Laser era in frequency standards and precision timing, spectroscopy …• Already providing lowest phase-noise, timing jitter

– fs jitter soon common place– Lowest phase noise microwave signals

• Some applications of stable sources and combs– new capabilities for science fundamental physics– Ultralow timing jitter, ultrafast sampling A/D, synchronization– Frequency standard precision spanning the spectrum 1 GHz to 500 THz +– Stabilized fs optical frequency combs enabling several new directions in

spectroscopy, Fourier synthesis

• Chip Scale Atomic Devices – practical route to bring atomic precision tofield devices– Combination of MEMS, diode lasers, atomic physics– Clocks, Magnetometers, Gyros ..