Stanford PNT hollberg Nov07 b - Stanford Center for Position ...

Sundial
Atoms and Lasers for Precision Timing and Position
Leo Hollberg
National Institute of Standards and Technology (NIST) , Boulder CO
Atomic
Astronomical
Pendulum
Harrison

Optical Frequency Measurements Group
NIST, Boulder
Optical Clocks
Chris Oates
Cold 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)
Chip Scale Atomic Devices
clocks, magnetometers …
John Kitching
Svenja Knappe (Germany)
Peter Schwindt (Sandia)
Vishal Shah → (Princeton)
Vladi Gerginov (Bulgaria)
Ying-Ju Wang (Taiwan)
Clark Griffith
Andy Geraci
Hugh Robinson
Liz Donley
Eleanor Hodby (England)
Alan Brannon (CU)
Brad Lindseth (CU)
Matt Eardley (CU)
Susan Schima
Lucas Willis (LSU, SURF)
Nicolas VanMeter (SURF)
•$$ NIST, DARPA-MTO, ONR-CU-MURI, NASA, LANL
fs Frequency Combs
Scott 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 Metrology
Richard Fox
NIST Opto-Electronics
Nate Newbury, Bill Swan ...

Accuracy of clocks through history
Verge & Foliot Balance
Year (AD)
Primary Caesium Clocks
Early Caesium Clocks
Quartz Crystal
Shortt
Reifler
Free Pendulum
Harrison’s Chronometer
Temperature Compensation
Barometric Compensation
Huygens Pendulum
Chinese Hydro-mechanical
Graham’s-Escapement
Cross Beat Escapement
1000 1200 1400 1600 1800 2000
Future
Fractional Error
1ps / d
1ns / d
1 µs / d
1ms / d
1s / d
1000 s / d
Δt/t
10 -15
10 -9
10 -3

Highest Accuracy Atomic Clocks

Current Microwave-Based Standards and Distribution
Hydrogen
Masers
and
Cesium
Clocks
NIST-F1
NIST
Measurement
System
Δf/f ~ 1x10 -15
for standards
and distribution
Rb and/or Cs
GPS
Communications
satellites
Radio
broadcasts
Approaching the limit for standards and distribution systems.
T. Parker et al.

Examples of Atomic Clocks for the Future Today ?
• Optical Atomic clocks – use lasers rather than
microwaves to probe atoms
• CSAC (Chip Scale Atomic Clocks) for hand held portable
systems
Microwave Atomic frequency Standard
Cs
Microwave
clock transition
Laser cooling
and detection
852 nm
9,192,163,707 Hz
Laser Cooling
and detection
(Blue or UV)
Optical Atomic frequency Standard
Optical ‘Clock
transition 10 15 Hz

Relative position, dimensional metrology, surveying instruments rely
on the fixed speed of light c and frequency references
discharge lamps, lasers and purely classical optics
Michelson Interferometer,
BIPM, Paris, circa 1910 ?
HeNe 633 nm
Frequency Lock
electronics
I 2
Lunar ranging w/
laser pulses
" =
c
n!

NIST F1, Cs atomic fountain clock
Primary frequency Std. of U.S.
S. Jefferts, L. Donley, T. Heavner, T. Parker

Feedback System
Locks LO to
atomic resonance
High-Q resonator
Quartz
Fabry Perot cavity
Local Oscillator
Generic Atomic Clock
Microwave Synthesizer
Laser
Δν
Atoms
υ
Counter
Detector
Ca
456 986 240 494 158

Advantages of Optical Clocks Quantum Projection Noise
Fractional Frequency instability ~
1 P
Cooling/
detection
transition
S
f
3 P or D
Clock
transition
0
f optical
microwave
! = observation time
N = number of atoms
10
!
10
0 !
15
10
5
10
• Large number of atoms 10 6 or more
• High signal/noise
• Possibility of lattices
# =
One atomic clock is always “perfect”
Two similar clocks -- hard to detect systematic errors
Different types of clocks can determine most accurate and stable
y
K
$ "
"
T
N
cycle
atoms
!
Candidate neutral atoms
Ca, Sr, Yb, Mg, H, Ag, Hg…
0
Δν
ν 0
ν

Laser source
Ca Oven
Optical Atomic Clocks
Cold Atom Optical Frequency Reference
I(f)
0
f r
Optical Synthesizer
Divider / Counter
f n = nf r
f
µ-wave out
optical out
Stable optical
Cavity

σ(τ)
Oscillator Stability
Ca
Optical
Cavities
1 fs
Cs
Ca projected
H-maser
Hg +
projected
GPS
1 day 1 month
0.5 Hz @
500 THZ

Fractional Frequency Uncertainty
1.0E-09
1.0E-10
1.0E-11
1.0E-12
1.0E-13
1.0E-14
1.0E-15
1.0E-16
1.0E-17
Accuracy of Atomic Frequency Standards - History
state-of-the-art Cs microwave
Infrared
Visible
Ion
Alk. Earth
1.0E-18
1970 1975 1980 1985 1990
Year
1995 2000 2005 2010 2015

1 P1 (4s4p)
423 nm cooling
Δν = 34 MHz
1 S0 (4s 2 ) m=0
Percent of Atoms Excited
40
30
20
10
Cold Calcium optical atomic clock
3 P1 (4s4p) m=0
657 nm clock
Δν = 400 Hz
0
0 2 4 6 8 10 12
Relative 657 nm Probe Detuning (MHz)
5x10 6 atoms
423 nm MOT
Demodulated Signal (V)
0.2
0.1
0.0
-0.1
-0.2
Ca
60 seconds data acquisition 400 Hz
linewidth
0 1000 2000 3000 4000
Relative Probe Frequency (Hz)

1 P1 (6s6p)
Atom number [a.u.]
Ytterbium optical atomic clock
- Excellent prospects for high stability and small absolute uncertainty
398.9 nm,
28 MHz
3 P0 : 578.42 nm,
~15 mHz
Clock Transition
full width ~ 4 Hz (Q >10 14 )
0.55
0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
-20 -15 -10 -5 0 5 10 15 20
Frequency offset [Hz]
Lattice
759 nm
3 P0,1,2 (6s6p)
3 P1 : 555.8
nm, 182 kHz
Chad Hoyt
Zeb Barber
Chris Oates
Candidates:
Sr, Yb, Ca, Hg

Allan deviation σ y (τ)
1E-14
1E-15
1E-16
Stability of two optical freq. ref: Yb and Ca
1 10 100
Averaging time (s)
1
0.1
Frequency precision [Hz]

Feedback System
Locks LO to
atomic resonance
High-Q resonator
Quartz
Fabry Perot cavity
Local Oscillator
Generic Atomic Clock
Microwave Synthesizer
Laser
Δν
Atoms
υ
Counter
Detector
Ca
456 986 240 494 158

Enthusiasm for Optical Atomic Clocks and fs Combs
Tara
Fortier
Scott
Diddams
Nobel Prize
2005
Jan Hall
Ted Hänsch

Count Optical Frequencies with Optical Frequency Combs
Ultra-short and repetitive pulses of light
20 fs
time
Ultrashort optical pulse, plus nonlinear fiber → Broad Spectum
Repetitive pulse train → Frequency Comb → “ruler for frequency/time”
Power
Wavelength
•Initial efforts/ideas: J. Eckstein, A. Ferguson & T. Hänsch (1978), V. P. Chebotayev (1988)

Self-Referenced Optical Frequency Sythesizer
I(f)
0
Microwave out
Jones, et al. Science 288, 635 (2000)
Ideas, existed many places, Telle &
Keller …, Udem, Hänsch …
f n = n f rep + f o
f o
f rep
x2 f 2n = 2nf rep + f o
Pump
f o
532 nm
convex
Optical Freq. Ref
f
Ti:Sapphire
Gain

The frequency of a mode is simply F N = N * f rep – f 0
Where N is and integer ~ 10 6
0
f r =1/ τ r.t.
f 0
f rep ~ 1000 MHz
0
Frequency

500 THz
Optical Oscillator
CW Laser Output
500 THz
fs Pulse Train
(Clock Output)
Diddams, et al.
~2 fs
1 ns
~5 x 10 5 Magnification
time

Hg +
~1 fs per
tooth
Mechanical Analogy of the Optical Clock
Femtosecond Laser Comb
1,000,000:1 Reduction Gear
(not to scale)
Microwave Output
~1 ns per tooth
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 of
fundamental 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 gas
detection… )
•Quantum information ( Ivan Deutsch …)
•Fourier synthesized arbitrary waveform generation

Optical
reference
f opt
M3
I(f)
PUMP
fs frequency combs as Optical Frequency Divider
Generation of microwaves with low phase noise
0
f µ-wave
M1 M2
f
Optical outputs
µ-wave out
OC
20 fs
I(f)
f µ-wave = f opt /N
time
1 ns
Microwave pulses
30
ps
Microwave comb w/
1 GHz mode spacing
Microwave frequency
f

L(f) dBc/Hz
-40
-60
-80
-100
-120
-140
-160
10 0
Low phase-noise microwaves, 10 GHz
atoms
Cavity kT
State of the art sapphire oscillator
10 1
10 2
Optical Frequency
Divider
10 3
Frequency (Hz)
Opt. Divider Data from Hollberg et al. proceeds IEEE MWP meeting Oct. 04
J. McFerran et al. Elect. Letter 2005
Hg+ optical cavity
State of the art microwave synthesizer
10 4
Photo detected shot-noise
10 5
10 6

Source Lab
Laser Source
563 nm
linewidth ∆n

I(f)
f rep
GPS
Optical Frequencies Measured via GPS
optical
x2
Self-Referencing
f unknown
Fox et al. Applied Optics, 05,
Even commercial systems now
available – CLEO/QELS trade show
f
R. Fox, S. Diddams NIST,
also similar work at NPL …
Red, 633nm I 2 – Stabilized HeNe laser

Next generation Grace
laser ranging ?
Advanced cold atom clocks or
Laser ranging/imaging in/from Space
T2L2
ESA
PARCS
NASA
HYPER, …
ACES
ESA

NIST Time and Frequency
John Kitching
Svenja Knappe
Vladislav Gerginov
Vishal Shah
CSAC
Susan Schima
Peter Schwindt
Clark Griffith
Brad Lindseth
CSAM
Ying-Ju Wang
Matt Eardley
Elizabeth Donley
Eleanor Hodby
Hugh G. Robinson
NIST Electromagnetics
John Moreland
Li-Anne Liew
Gyro
CSADs Team
Dir.
Coup.
MEMS
University of Colorado
Z. Popović
A. Brannon LO
J. Breitbarth
J. Maclennan Wall coatings
Y. Li

Chip Scale Atomic Devices
CSAC (clock), CSAM (magnetometer), CSAG (gyro)
Optical excitation, atoms, MEMS, VCSEL lasers, low power
Battery powered devices, connect to application requirements

Cell Fabrication: Anodic Bonding
• Preform created by KOH etching or
DRIE of Si
• Pyrex bonded on one side with
anodic bonding
• Cell preform filled with Cs
– BaN 6 + CsCl → BaCl + Cs + 3N 2
@ 150 ºC
• Diced cells made at NIST using the
anodic bonding technique
– Interior: 1 mm x ∅ 0.9 mm
– Exterior: 1.33 mm x (1.45 mm) 2
L. Liew, et al., Appl. Phys. Lett., 84, 2694, 2004.
1 mm
1 mm
Pyrex 7740 (125 µm)
Silicon (375 µm)
Pyrex 7740 (200 µm)

4.2 mm
1.5 mm
NIST Chip-Scale Atomic Clock: 2004
1 mm
S. Knappe, et al., Appl. Phys. Lett. 85, 1460 (2004).
Volume:
9.5 mm 3
Cell volume:
0.81 mm 3
Cell temp:
85 ºC
Heating
power:
75 mW
Stability:
σ y (1 sec.) =
2.5×10 -10

Short-term stability: 4×10 -11 @ 1 sec
S. Knappe, et al., Opt. Express 13, 1249-
1253 (2005).
Relative Frequency
(10 -9
)
4
2
0
-2
-4
CSAC Frequency Stability
1 mm
20000 30000 40000 50000
Time (sec)
Longer-term stability: 1×10 -11 @ 1 hr
S. Knappe, et al. Opt. Lett. 30, 2351-2353
(2005).
Allen Deviation, !f/f
10 -9
10 -10
10 -11
10 -12
Drift
Cs CSAC: -2 x 10 -8 /day
87 Rb Cell:

(A Very Rough) Oscillator Comparison
Adapted from figure by R. Lutwak, Symmetricom
Quartz Crystal
Oscillators

Applications of Microfabricated Atomic Clocks
• Size (1 cm 3 )
• Power (30 mW)
Integration in portable,
battery-operated devices
• Precise timing: higher-performance, more reliable operation
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 < 4
τ 3
τ 4
(τ 1 , τ 2 , τ 3 , τ 4 )
(x, y, z, t)
Satellites
τ 2
GPS
Receiver
Atomic
clock
τ 1

Commercialization of Chip-Scale Atomic Clocks
Symmetricom/Draper/Sandia
(courtesy R. Lutwak)
RF output
< 10 mW
power requirement
Complete functioning CSACs
10 cm 3
108 mW
5×10 -11
@ 100 s
Honeywell
(courtesy D. Youngner)
solder
titanium getter
vcsel
optical path
optics
vacuum
Trans -Impedance Amp
gold reflector
rubidium +AR/N2
solder
Photo -detector
top top cap cap
wafer wafer
cavity cavity cavity
wafer wafer wafer
bench bench bench bench wafer wafer wafer wafer
1.7 cm 3
57 mW
4×10 -12
@ 1 hr

Magnetometry with Chip-Scale Devices
Atom Energy
Hyperfine
splitting
-2 -1 0 +1 +2
mFj ћω HF
Zeeman splitting
ћω L = ½µ ΒΒ

M X Magnetometer
• Improved sensitivity; no GHz oscillator
Energy
D1
Optical
Microwave
Vapor
cell
λ/4
Filter
A. Bloom, E. Alexandrov, A. Weis, and many others
ν hf
Photodetector
B
Semiconductor
Laser
ΔB
RF
Coils

Heater Currents
Laser Current
Local Oscillator
Driving RF Coils
Loop
Filter
Data
Acquisition
CSAM Operation
Photo-
Diode
Signal
Lock-in
Amplifier
2 kHz Sidebands
Width = 1.7 kHz
or 243 nT

M X CSAM Performance
Sensitivity Frequency Response
F 3dB = 1 kHz

Magnetocardiography with a CSAM
• At U. Pittsburgh with Dr. V. Shusterman
• Mouse anaesthetized, placed near CSAM
• ECG and MCG signals recorded
(a) (b)
4.5 mm
1
2
1.7 mm
6
5
4
3

CSAM Sensitivity Comparison
Adapted from R. L. Fagaly,
Rev. Sci. Instrum., 77 (2006).
SQUID
Susceptometry
Geophysical
Magnetocardiography Transient
Electromagnetics
Magnetic Anomaly
Detection
Non-Destructive Test and Evaluation
2004
Magnetoencephalography
87 Rb, 1 mm 3 atom shot noise
2006
2005
High Tc SQUID
Low Tc SQUID

Nuclear Spin Gyroscopes
• Much work in 1970s and 1980s
– Fraser (1963), Bayley, Greenwood, Simpson (1973)
– Commercial development: Litton, Singer-Kearfott, TI
Alkali
atom
Spin
Exchange
129 Xe
S (V)
Noble gas
atom
Lock In signal
Fit includes linear drift
f=y0+c*x+a*exp(-x/d)*cos(2*3.14159265359*x/b)
-0.2
-0.3
-0.4
-0.5
-0.6
-0.7
1e-1
1e-2
1e-3
1e-4
T 2 ~ 6 s
-0.8
0 5 10 15 20
t (s)
FFT of Lock-In Signal
! = 100 us, S=200 mV
Ω R
M ng
1
B 0
M Al
N B0N
R B !
! + " 0
ΔB 1 ΔB 2
100 µs
58 ms
Time
PD

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 to
field devices
– Combination of MEMS, diode lasers, atomic physics
– Clocks, Magnetometers, Gyros ..