precision / atomic clocks and fundamental tests in … clocks and fundamental tests in physics ......
Post on 03-Apr-2018
225 Views
Preview:
TRANSCRIPT
1
Atomic clocks and fundamental tests in Physics
Gaetano Mileti, Pierre Thomann, Sebastien Bize, Christophe Salomon, Claus Laemmerzahl
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 1 -
Precision / Stabilityin seconds
per day
1 ns
1 s
100 psAtomic clocks
(1950)
Hydrogen
Maser,
Caesium beam,
Rubidium clock
Quartz oscillators
10 ns
10 ps
The metamorphosis oftime measurement
Marine chronometers Space atomic clocks
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 2 -
Tower clocks (1300)verge-and-foliot mechanism
10 s
1000 s
Huygens Pendulum (1650)pendulum
Marine chronometers
(1750), Harrison
1 ms
(1930)
1 s
Earth rotation
-3000 -1500 -170 800 1300 1600 19001700 2000
Program of lectures
February 25 Introduction and vapor-cell atomic clocks
G. Mileti, Université de Neuchâtel
March 4 H Masers and primary frequency standards
P. Thomann, Université de Neuchâtel
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 3 -
March 11 Optical frequency standards
S. Bize, SYRTE Paris
March 18 The ACES mission on the ISS
C. Salomon, ENS Paris
March 25 Atomic clocks in space for fundamental tests
C. Laemmerzahl, Universität Bremen
Essential specialized bibliography
• Jacques Vanier, Claude Audoin, “The Quantum Physics of
Atomic Frequency Standards”, Bristol: Adam Hilger, 1989.
• Claude Audoin, Bernard Guinot, Stephen Lyle, “The
Measurement of Time: Time, Frequency and the Atomic
Clock ”, Cambridge, (Original in french : Masson, 1998).
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 4 -
• Fritz Riehle, “Frequency standards – Basics and
applications”, Wiley-VCH, 2005.
• Special issue of Metrologia: “Special issue: fifty years of
atomic time-keeping: 1955 to 2005”, Volume 42,
Number 3, June 2005.
Introduction, vapour-cell atomic clocks and applications
Gaetano Mileti
(gaetano.mileti@unine.ch)
Laboratoire Temps – Fréquence (LTF)
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 5 -
Laboratoire Temps – Fréquence (LTF)
(http://www2.unine.ch/ltf)
Institut de PhysiqueFaculté des Sciences
Université de Neuchâtel
Plan of the presentation
I. Introduction on the measurement of time
II. Stabilized oscillators and atomic clocks
III. Commercial Rubidium clocks and applications
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 6 -
III. Commercial Rubidium clocks and applications
IV. Current research on vapour-cell standards
2
Essential bibliography related to this lecture
Introduction on the measurement of time:
• Chapters 1-2-3 of book F. Riehle, Wiley-VCH, (2005)
Rubidium clocks:
• Chapter 8 of book J. Vanier and C. Audoin, Adam-Hilger, Bristol (1989)
• Article of J. Camparo, Physics Today, November (2007)
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 7 -
From the lecturer:
• PhD thesis, Université de Neuchâtel (1995)
• ESA bulletin, vol. 122 (May), p. 53, (2005)
• Proc. SPIE, vol. 5830, p. 159, (2005)
• Comptes-rendus du Congrès Intern. de Chronométrie, p. 91 (2007)
• Journal and Web site of the Swiss Physical Society, July, (2008)
I. Introduction on measurement of time
1. Measurement of time, calendars, clocks and frequency standards
2. Time and frequency instability
3. Mechanical and piezoelectric oscillators
4. Accuracy and stability
5 First overview of applications and needs
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 8 -
5. First overview of applications and needs
What is a clock?
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 9 -
Picture:
View from
Observatoire
Cantonal de
Neuchâtel,
founded in
1858
“Clock = Oscillator + Counter”
~
“Oscillator”
Based on a periodical event,
supposedly “regular” and having a
period T (earth, pendulum, spring,
quartz, etc.)
Frequency f = 1 / T
14:32 26
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 10 -
9 192 631 770
“Counter”
Able to count the oscillations and
display the result in some manner
(escapement, gear, dial, hands, etc.)
“in” and/or “out” of the standard“Reference”:
Sometimes used to stabilize the oscillator and/or the clock
1. Measurement of time, calendars, clocks and
frequency standards
Examples of natural periodical events: earth rotation,
moon phases, seasons, etc. but also: heart beat,
“biological” time, etc.
Examples of needs and applications: agriculture, social
life (daily weekly annually etc ) sailing
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 11 -
life (daily, weekly, annually, etc.), sailing
(longitude), electronic equipment,
telecommunications, satellite navigation, etc.
Examples of developed tools: calendar (Julian,
Gregorian, …), sundial, clepsydra, tower clock,
pendulum, telescope, wrist watch, chronometer,
atomic clock…
Some concepts on measurement of time:
Julian date JD: used by astronomers. Day number
since 4713 BC (day starts at noon).
Modified Julian Date MJD: used in T&F metrology,
earth rotation studies, space research (MJD =
JD - 2400000.5).
Jan. 1st 2000 noon
= 2451545.0 JD
MJD = 0 on Nov. 17
1858 at 0 AM
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 12 -
Length Of the Day LOD and True solar time:
defined by earth rotation on its axis.
Universal Time (UT): agreed international time
scale referred to the first meridian.
The LOD varies by
30 minutes in 1 year
UT, UT1, UT2, UTC,
GMT
3
Definition in SI system
The second is the duration of 9 192 631 770periods of the radiation corresponding to the transition between the two hyperfine levels of
the ground state of cesium 133 (1967)
→ Atomic Time (TAI)
Definition of the second (see lecture 2 for details)
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 13 -
Hzh
EEFrequency 770631192912
0
F=4
F=3
6 S½
Atomic time (TAI) and astronomical time (UTC)
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 14 -
Leap second
Ideal and real oscillators
Ideal “oscillator” (or frequency standard)
Black box having an input (power supply) and an “ideal” output: for instance an absolutely
pure (accurate and stable) sinus with amplitude A and frequency 0
)2cos( 0tA
Spectral domain
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 15 -
Real “oscillator”
The amplitude and the frequency of the output fluctuate. These instabilities are observed and described by various techniques in the “time
domain” and in the “frequency domain”.
)( 02)()( ARe
tjettSignal
)( 02)()( ARe
tjettSignal
( ) ( ) ( ) ( ( ) )( )
t t j q t t ej tp 1
02
)()(:
ttxerrorTime
00 td
)(d
2td
)(d)(:
1
tttyerrorfrequencyNormalized
x
where
Oscillator model
Atomic clocks:
10-10 - 10-16
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 16 -
)()(: 0 ttfrequencyMeasured
nsfluctuatiorandomticdeterminist :)(
(t) is a random non stationary process
Tt
tTdtt
TLim )(
1 In general diverges
td
)(d
2)(
10
tty
Allan deviation)()(: 0 ttfrequencyMeasured
0
)(:
tyerrorfrequencyNormalized
1
)(1 K
K
t
tK dttyy
ld22
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 17 -
generalindivergesyvarianceTrue ky22:""
Two-samples variance (Allan variance):
212
12 )()( kky yy
deviationAllany :)(
How to measure the Allan deviation (normalized frequency fluctuations)
of a an oscillator? By comparing it to a better oscillator!
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 18 -
Source: John Vig, tutorial on «Quartz crystal resonators and oscillators»
4
Allan deviation () and noise processes (f)
y()tells us how our
oscillator
compares to an
ideal one over the
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 19 -
• Different types of noise processes affect differently the Allan deviation;
• Different applications require different (in)stabilities at given time scales
timescale
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 20 -
Source: John Vig, tutorial on «Quartz crystal resonators and oscillators»
10-12
10-11
10-10Cs beam, magneticCs-beam, laser H-maser, activeH-maser, passiveRb cell, lampRb or Cs cell, laser CS cold
dev.
Example: frequency standards for satellite navigation
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 21 -
10-16
10-15
10-14
10-13
1 10 100 1000 104 105 106 107
Time interval (s)
Alla
n
For 30 cm accuracy
Maximal Time error:
1 nanosecond for
1s < t < 20’000 s
1410)000'20( sy
3. Mechanical and piezoelectric oscillators
Examples of oscillators that have been developed:
• The Foliot (~ 1300)
• The Pendulum (1657)
• The “Balancier spiral” (1673)
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 22 -
• … longitude on sea challenge (marine chronometers)
• 1950-1960: electromagnetic excitations of a tuning fork (diapason)
• 1960-1970: quartz oscillators
• More recently: MEMS-based oscillators
Simplified behavior of quartz oscillators
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 23 -
Source: John Vig, tutorial on «Quartz crystal resonators and oscillators»
Oscillating frequencies
• The Pendulum 1 Hz
• The “Balancier spiral” 4 Hz
• Tuning fork (diapason) 300 Hz
• Watch quartz 32’768 Hz
• Microwave atomic transition 1-10’000’000’000 Hz
• Optical atomic transition 100-1000’000’000’000’000 Hz
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 24 -
p
In general: the higher the frequency, the better the time resolution
But:
• The resonance width and quality factor also matters
• The signal-to-noise ratio
• The problem of “counting”
5
4. Accuracy and stability
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 25 -
How to measure / evaluate the stability and accuracy?
• By comparing to a more stable and/or accurate oscillator
• Statistical and non-statistical analysis (see lecture # 2 on primary standards)
Source: John Vig, tutorial on «Quartz
crystal resonators and oscillators»
5. First overview of applications and needs
Agriculture (seasons) ~ 1’000’000 s
Calendar (solstices, equinoxes) ~ 100 ’000 s
Daily activities (professional, social, etc.) ~ 1’000 s
Determination of the longitude (sea navigation) ~ 1 s
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 26 -
Common electronic and telecommunication devices ~ 0.01 s
Advanced telecommunication devices ~ 0.000’001 s
Satellite navigation ~ 0.000’000’001 s
Scientific research and primary metrology < 0.000’000’000’1 s
Need of atomic clocks (in the device or to calibrate the device)
II. Stabilized oscillators and atomic clocks
1. Basic principle of a stabilized oscillator
2. Basic principle of an atomic clock
3. Fundamentals on magnetic resonance
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 27 -
4. Advantages and categories of atomic clocks
5. Applications of atomic clocks
1. Basic principles of a stabilized oscillator
Example 1 of a stabilized oscillator:
pendulum periodically stabilized
after earth rotation observation
Example 2 of a stabilized oscillator:
wrist-watch periodically stabilized
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 28 -
wrist watch periodically stabilized
after comparison to a more stable /
accurate clock (tower clock)
Examples 3 of a stabilized oscillator:
quartz oscillator locked to a GNSS
signal (GPS, GLONASS, GALILEO …)
2. Atomic clock (stabilized quartz)
AtomsQuartz oscillator
Reference for the user (5 MHz)
Interrogation
Feed-back
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 29 -
Definition in SI system
The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of
the ground state of cesium 133 (1967)
Hzh
EEFrequency 770631192912
0
F=4
F=3
6 S½
This would be the frequency of an atomic
clock in which the atomic transition is not
perturbed and the stabilisation “perfect”
9 192 631 770 Hz
Magnetic resonance
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 30 -
Typically 5 or 10 MHz
6
Lock-in detection
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 31 -
Resonance line-width, line Q, signal-to-noise ratio and frequency stability
0.08
0.10
0.12
0.14
ht [
V o
n 1
0k
]
1
0
: resonance «duration»
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 32 -
5.304x106
5.306x106
5.308x106
5.310x106
5.312x106
0.00
0.02
0.04
0.06
Tra
nsm
itte
d lig
h
6.84 GHz - Synthesiser frequency [Hz]
21
).(
2.0
NSQI
y
J. Vanier, L. Bernier, IEEE Trans. on Instr. and Meas., Vol. IM-30, No 4, Dec. 1981
0
0
Q
3. Fundamentals on magnetic resonance
• Magnetic moment interacting with
a magnetic field
• Static :
)()()( tBtmtmdt
d
B
m
oB
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 33 -
Larmor precession
• +rotating magnetic field
magnetic resonance
o
00 B
0
)(1 tB
oB
oB
s
pulse
pulse)(1 tB
The classical Bloch equations and NMR
2
)())()(()(
T
tmtBtmtm x
xxdt
d
2
)())()(()(
T
tmtBtmtm y
yydt
d
))(( mtmd
Stationary solutions
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 34 -
1
0 ))(())()(()(
T
mtmtBtmtm z
zzdt
d
timerelaxationtransverseT
timerelaxationallongitudinT
:
:
2
1
22121 /12 TTTFWHM
(collisions and magnetic inhomogeneities)
Spin 1/2+ magnetic field
(classical or quantum)
Atome+ laser
(dipolar approximation)
Atome+ champ RF
852 nm(3.5 108 MHz)
9.2 GHzB
S
Generalizing the Bloch equations
momentelectricatomicd :
momentmagneticatomic:
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 35 -
.
effBS
BSdt
Sd
BSH
fofofo Bb
dt
bd
EdH
ˆˆ
fmfmfm Bb
dt
bd
BH
ˆˆ
RFB
B
1
00
Laseropt
opt
Ed
11
120
RFRF
RF
B
1
1
120
momentelectricatomicd : momentmagneticatomic:
Generalized Bloch equations
1
w
v
u
S
S
S
z
y
x
)(
)Im(
)Re(
1122
21
21
différencepopulation
momentdipoletheofcomponentquadraturein
momentdipoletheofcomponentphasein
12
222
1212
2
120
1
1
TTT
wust
Stationary solutions
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 36 -
01
12
122
2
1
1
wwT
vw
wvT
uv
vuT
u
222
1212
2
2
1212
0
222
1212
2
212
0
11
1
TTTTT
ww
TTTT
wv
st
st
0
7
The Bloch vector (Semi-classic)
2E
1E
Atom (or ensemble of atoms)
Interacting field (RF, microwave, optical)
Bloch vector (fictitious spin)
tie
12 EE
spopulationofdifference
quadratureindipoleatomic
phaseindipoleatomic
w
v
u
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 37 -
• The state of an atom (2 levels) may be represented with
a vector (“Bloch vector”, or “Fictitious spin”) and its
behavior when interacting with a resonant field as a
magnetic moment in a magnetic field.
• Microwave transitions, optical transitions, /2 pulses, etc.
s
R. Feynman, F. Vernon, R. Hellwarth, “Geometrical representation of the Schrödinger equation for solving Maser problems”, J. App. Phys, Vol. 28, p. 49, (1957).
Examples of Bloch vectors
2E
1E
Atoms in fundamental state
(no field)
1
0
0
w
v
u
s
EAtoms after
it ti
0u
oB
s
oB
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 38 -
2E
1Eexcitation
(and field switched off)
1
0
w
vss
2E
1E
Atoms after excitation
(and field switched off) quantum
superposition of states
0
)sin(
)cos(
0
0
t
t
w
v
u
s
oB
s
General scheme (or sequence) in atomic clocks:
- Have the atoms available and as isolated as possible from
the “outside” undesired interactions / perturbations;
- Put (or select) as many atoms as possible atoms in one
(of the two) levels;
- Perform the “magnetic resonance”;
0
0
0
s
1
0
0
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 39 -
Perform the magnetic resonance ;
- Detect the result of the “magnetic resonance” (level
transition) ;
- Apply the necessary correction to the quartz oscillator
Open loop (synthesizer) or closed loop mode
Magnetic resonance allows spin flip.
It is a frequency selective phenomenonS
ign
al
Linewidth
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 40 -
In an atomic clock you exploit this phenomenon to frequency stabilise a quartz oscillator
In each type of clock it is realised on different species, in various configurations and with different detection techniques
Probing frequency
Alkali atoms in “microwave” clocks
• Hydrogen-like atoms: 1 unpaired electron
• Hyperfine structure: interaction of
• Simplified structure:
nucleousewith
P3/2
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 41 -
• Ground state:S1/2
P1/2
3/2
lumière(1014 Hz)
micro-onde(109 -1010 Hz)
0
0
0
w
v
u
s
87Rb133Cs
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 42 -
5S1/2
F=1
F=2mF = 0
mF = -1
mF= -2
mF = 1
mF = 2
mF = 0
mF = -1
mF = 1
6.8346 GHz5S1/2
F=2
F=3
3.0357 GHz
mF = 0
mF = -1
mF= -2
mF = 1
mF = 2mF = 3
mF = -3
mF = 0
mF = -1
mF= -2
mF = 1
mF = 2
87Rb
85Rb
6S1/2
F=3
F=4
mF = 0
mF = -1
mF= -2
mF = 1
mF = 2mF = 3
mF = -3
mF = 0
mF = -1
mF= -2
mF = 1
mF = 2mF = 3
mF = -3
9.1926 GHz
mF = 4
mF = -4
133Cs
8
4. Advantages of atomic clock (over quartz)
• All (isolated) atoms of the same element and isotope have an
identical structure (energy levels);
• These atoms provide a stable and accurate reference to frequency
stabilize an oscillator;
• It is a fundamental and intrinsic property;
• Less sensitive to environmental effects (temperature, vibrations, etc.)
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 43 -
• Less aging, drift, warm-up time and retrace effect.
But:
• These atoms still interact with their environment (in and out of the
clock) which is responsible of the differences and drifts between the
standards;
• These atoms usually move: Doppler effect, collisions, etc.
• Primary (Cs) – Secondary → lecture 2 (P. Thomann)
Categories of atomic clocks (or frequency standards)
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 44 -
• Passive – Active (H-Maser) → lecture 2 (P. Thomann)
• Commercial (Rb, Cs, H) → lectures 1-2 (G. Mileti, P. Thomann)
• Laboratory – “In development” → all lectures
• Microwave – Optical → lecture 3 (S. Bize)
5. Applications of atomic clocks (general)
4 Radioastronomy, Geodesy
(VLBI, Radioastron, etc.)
4 Scientific Research, Instrumentation
(Microgravity, ACES, HYPER, etc.)
4 Navigation & Positioning
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 45 -
g g
(Galileo, GPS, GLONASS, etc.)
4 Telecommunications
(Networks synchronisation, etc.)
4 Metrology, Time scales
(Primary and secondary standards, H-Masers)
III. Principle of commercial Rubidium clocks and applications
1. The Rubidium frequency standards
• Principle of the clock
• Examples of realizations
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 46 -
a p es o ea at o s
2. Applications
• Navigation
• Telecommunications
1. The Rubidium frequency standard
Heart of the clock: a Rubidium buffer gas cell
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 47 -
5S1/2
F=1
F=2mF = 0
mF = -1
mF= -2
mF = 1
mF = 2
mF = 0
mF = -1
mF = 1
6.8346 GHz
87Rb
Rb partial pressure: 10-5 torr
(10-11-10-12 atoms)
Basic interactions (of the atoms in the cell)
Each atom in the vapor undergoes the following interactions:
• Collisions:
buffer gas, other atoms, walls
• Static magnetic field 5S1/2
F=2mF = 0
mF = -1
mF= -2
mF = 1
mF = 2
6 8346 GHz
87Rb
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 48 -
Static magnetic field
Collinear with laser propagation
• Resonant interaction with the optical beam
• Resonant interaction with a microwave fieldS
P
light
-wave
F=1mF = 0
mF = -1
mF = 1
6.8346 GHz
RFBH
ˆ
EdH
ˆˆ
9
Lampe Rb87 filtre Rb85 cellule Rb87
Optical pumping (hyperfine)
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 49 -
S
P
Thermal equilibrium
S
P
Complete optical pumping
S
P
Partial optical pumpingS
P
Hyperfine optical pumping
20
25
30
A]
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 50 -
-4 -2 0 2 4 6 80
5
10
15
20
D2 lines of Rb87
F = 1F = 2
Pho
tocu
rren
t [mA
Laser diode frequency [GHz]
Note:
With a slow frequency scan, this spectrum is visible only if there are collisions that “destroy” optical pumping.
Absorption spectrum of natural rubidiumD2 line (780 nm)with 30 mb of nitrogen
Rb 85 - F=2
Rb 87 - F=2
Rb 85 - F=3
S
P
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 51 -
Rb 87 - F=1
Optical frequency detuning [GHz]0 2 4 6 8
excitation d’une lampe 87Rb avec un oscillateur RF (~120 MHz)
filtrage isotopique par une cellule 85Rb
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 52 -
filtrage isotopique par une cellule 85Rb
+
Lampe Rb87
filtre Rb85
cellule de résonance Rb87
détecteur
cavité micro-onde
Double resonance
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 53 -
5.304x106
5.306x106
5.308x106
5.310x106
5.312x106
0.108
0.112
0.116
0.120
0.124
0.128
Tra
nsm
itte
d li
gh
t [V
on
10
k]
6.84 GHz - Synthesiser frequency [Hz]
S
P
Double resonance
light
-wave
iRb
iRbI
hd
W cm
Jcm s ( )
( )[ / ]
[ ][ ] [ ]
22 1
][)(1069,2)(
)()( 22 cmg
g
g
o0
2natural width 5 9 MHz
Interaction with light: line shapesAbsorption rate:
number of photons absorbed per second by the atom (in level i)
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 54 -
g o
o o
( )( ) ( )
22 2
natural width 0 5.9 MHz(Lorentzian)
For an atom at rest
22ln24ln22
ln2)(
)(20
20
cM
Tkg Be
Doppler (inhomogeneous)
broadening: (Gaussian) 527 MHz, for Rb @ 60°C
10
4
6
8
10
12
14
16
18
20
= 200 MHz
= 400 MHz
= 600 MHz
= 1 GHz
Rubidium 87 - D2T = 60°C = 527 MHz
= 100 MHz
No broadening
nesh
ape
func
tion
g(
) [10
-10 .s
]
Buffer gas(Lorentzian)
Homogeneousbroadening
Convolution of a
Optical absorption line in a buffer gas cell
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 55 -
-2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.50
2
4Li
Optical frequency detuning [GHz]
g ei
erfc i( )
( )( )( )
( )
22 2
20
0ln2ln2 ln2
ln2 ln2
Re
Convolution of a gaussian with a
Lorentzian
Voigt profile
curr
en
t
CO
21-
23C
O 2
2-2
3
CO
32
-34
CO
33-
34
23 Mode hop
Laser reference cell
Rb 87 Rb 85
Experimental example
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 56 -
Pho
to
Piezo voltage
34
Laser lockingrange for theprel. exp. on
laser stabilisation
Laser lockingrange for the
clock
200 MHzResonance cell transmission(modified TNT RAFS)
Laser reference cell(natural Rb)
Rate equations with a 3-levels model
I
III
1
II
III Bloch equations approach
« Fictitious » spin
U: dipole component in phaseV: dipole component out of phase
)-(
0//1
1
vw
wvuv
vuu
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 57 -
II
tiIIIIIIRb
IIIIII
tiIIII
III
IIIIII
tiIIII
III
IIII
eii
e
e
)()(
)(Im)(
)(Im)(
12
12
1
12
1
2
22
22
2
2
1
1
V: dipole component out of phaseV: difference of population
I II ( ) ( )
Im
ll 0 14 I IIi te
i i Spin Exchange i Wall Collisions i Buffer GasCollisions / / / i 1,2
)(22 21// III
Broadening (relaxations):
Rate equations (equivalent to Bloch equations):
Note: here the interaction with light is described as a relaxation process
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 58 -
tiIII e
0 2 ( )I II ll
( )
1I II Rb I II
i ti i e
2
2
0 22)(1
Rb
2124 / ll
Stationary solution:
300
400
500
600
c si
gnal
wid
th [
Hz]
Exemple expérimentalAvec une celluleCylindrique de 1-2 cm3
Parois
Gaz + Spin-Exchange
Collisions (relaxations)
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 59 -
0 20 40 60 80 1000
100
200
1° h
arm
onic
Nitrogen pressure [mbar]
variation du flux d'énergie
lumineuse
=
nombre d'atomes rencontrés par
les photons
x
nombre de photons absorbés par atome
et par seconde
x
énergie d'un photon
[W / cm2] [1 / cm2] [1 / s] [J]
I n l hI I Rb
Measured signal (locally)
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 60 -
n l hII II Rb
222
222
)(442
)()(
Rb
IIIIIIIIIRbhlnI
llll
Linearabsorption
Opticalpumping
Micro-wave
Clock signal
11
0.124
0.128
on
10
k]
The double resonance (DR) signal
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 61 -
5.304x106
5.306x106
5.308x106
5.310x106
5.312x106
0.108
0.112
0.116
0.120
Tra
nsm
itte
d li
gh
t [V
o
6.84 GHz - Synthesiser frequency [Hz]
Photons:
– 2·1012 / (s ·mm2)
incident
– 6·1011 / (s ·mm2)
transmitted
– 1.5·1011 / (s ·mm2)
Double Resonance
Rubidium clocks developed in Neuchâtel (~ 1985 to ~ 1996)
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 62 -
Commercial production for ground and space (Temex, now Spectratime)
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 63 -
GPS (USA) GLONASS (RU) GALILEO (EU)
Space Rubidium clocks
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 64 -
Other similar developments:
Rb clock for Cassini-Huygens mission, China (Wuhan, etc.) and Japan (Anritsu, etc.)
4. Rubidium clocks applications
• Satellite navigation
In space: Rubidium, passive Hydrogen Maser, thermal Cesium
On earth: (quartz), Rubidium, thermal Cesium, active / passive H Masers
GIOVE-A (DEC 05) GIOVE-B (2007)
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 65 -
Rubidium clocks for Galileo
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 66 -
Source: Pascal Rochat et al., SSOM meeting in Engelberg, 2007
12
Galileo system
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 67 -
Source: Pascal Rochat et al., SSOM meeting in Engelberg, 2007
Other applications of Rubidium clocks
4 Communications:
4 SDH (Synchronous Digital Hierarchy) CCITT G811,G812
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 68 -
4Mobile communications base stations reference clock 4 Spread Spectrum secure radio communication systems4 Digital Radio&Video Broadcast systems (DRB , DVB)
4 Instrumentation:
4 Telecom SDH synch. Test sets , Cellular base stations test sets …4 Synthesizers, Counters , Laboratory , Metrology4 GPS time receivers.
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 69 - 3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in Physics
G. Mileti, Introduction and vapour cell standards, 25.02.2010 - 70 -
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 71 -
+ price !
IV. Current research on cell standards
1. Use of tunable and frequency-controlled laser diodes
• Tunable and frequency-stabilized laser diodes
• The laser-pumped Rb clock
• Use of wall-coated cells
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 72 -
2. CPT cell standards and chip-scale atomic clocks
• Coherent Population Trapping
• Chip-scale atomic clocks
3. Summary and conclusions
13
Prof. P. Thomann (directeur) Dr. G. Mileti (DR, dir.- adjoint)
Dr. C. AffolderbachDr. E. Breschi
Dr. G. Di Domenico Dr. D. Hoffstetter
Dr. A. Joyet Dr. R. Matthey
Dr. S. SchiltDr. C. Schori
T. Bandi (doctorant)
Laboratoire Temps-Fréquence
Université de Neuchâtel
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 73 -
T. Bandi (doctorant)V. Dolgovskiy (doctorant)
D. Miletic (doctorante)L. Devenoges (doctorant)
M. Pellaton (doctorant)N. Bulatovic (doctorant)
F. GruetJ. Di FrancescoM. Durrenberger
P. Scherler M. Vallery-Muegeli
(http://www2.unine.ch/ltf)
1. Use of tunable laser diodes
Lampe Rb87 filtre Rb85 cellule de résonance Rb87
détecteur
cavité micro-onde
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 74 -
6.8 GHz
Rb87 Discharge lamp(several lines, > 1 GHz wide)
Laser (1 line, < 100 MHz wide)
3 GHz
Rb85 Optical filter
Potential advantages:
• More efficient pumping
• Improved S/N
• Long term stability
• Power / Weight / Volume
• Redundancy
Examples of Laser diodes
Solitary Fabry-Perot (FP)
Extended cavity lasers (ECDL)
Distributed Bragg Reflectors (DBR)
Distributed Feedback (DFB)
FP with DBR optical fiber
V ti l C it S f E itti (VCSEL)
1.50um
ECDL
FP (RWL)
Tuneable and frequency-controlled diode lasers
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 75 -
Vertical Cavity Surface Emitting (VCSEL)
MEMS based ECDL and VCSELs
Discrete mode lasers
Etc.
780, 795, 852, 894nm
Single, mode, mode-hop free tuning
Typical specs: 5-10 mW, LW < 5 MHz
Low intensity and frequency noise
DFB
DBR
VCSEL
Potential advantages of stabilized lasers in
atomic clocks
• More efficient atomic state preparation / selection:
Examples: optical pumping in Rb, Cs, Maser
• Improved detection of atomic states (S/N):
Examples: optical pumping in Rb, Cs, Maser
• Possibility to slow (cool) or trap atoms
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 76 -
Examples: cold atoms frequency standards
• Explore new physical phenomena
Examples: Coherent Population Trapping
• Miniaturization, etc.
Open issues: availability, reliability, cost, etc.
Diode &collimator
Tiltable support:grating & optical isolator
• beam collimation
• grating angle
sin2 a
• Cavity length
m
L
2
Extended-cavity diode lasers
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 77 -
Piezo
Laser output
Exam
ple
1:
het
erodyn
e fr
equen
cy s
pec
trum
Laboratory ECDL vsLaboratory ECDL ESA-ECDL vs DBR ESA-ECDL vs DFB
133.2 133.6 134.0 134.4-39
-38
-37
-36
-35
-34
-33
550 kHz
dB
m
F i f [MH ]
129 130 131 132 133 134 135 136 137 138 139-66
-65
-64
-63
-62
5 MHz
dB
m
132 133 134 135 136 137 138-38
-36
-34
-32
-30
-28
2 MHz
Am
plitu
de [d
Bm
]
Fourrier frequency [MHz]
Laser spectral cacterisation
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 78 -
Exam
ple
2:
mode-
hop
e fr
ee t
unin
g r
ange
Laboratory ECDL DBR DFB
Fourrier frequency [MHz] Fourrier frequency [MHz]29.05.2003 15:27:57Fourrier frequency [MHz]
>> 15 GHz
Ab
sorp
tion
Wavelength
8 GHz
wavelength
Mode hop
Rb 87 Rb 85
4 GHz
Ph
oto
curr
ent
Wavelength
14
10-10
10-9
Spec Rb clock Doppler sub-Doppler
freq
uenc
y y
()
Laser frequency stabilisation
-50 0 50 100 150 200 250
-0.1
0.0
0.1
0.2
sig
nal d
'err
eur
Uer
r (V
)
fréquence laser (MHz)
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 79 -
100 101 102 103 104 105
10-13
10-12
10-11
Sampling time (s)
Alla
n d
evi
atio
n of
the
lase
r
Compact and frequency-stabilized laser head
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 80 -
C. Affolderbach, G. Mileti, A compact laser head with high-frequency stability for Rb atomicclocks and optical instrumentation, Review of Scientific Instruments, Volume 76,073108, (2005)
Physics package(200cm3)
Volume for control electronics(300cm3,
• adapted resonance cell,
• lamp removed,
(empty volume!)
Laser-pumped Rb prototype (Neuchâtel)ESA-funded project
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 81 -
Stabilised laser head:
(300cm ,currently empty)
RAFS resonator module:
(empty volume!)
C. Affolderbach, F. Droz, G. Mileti, Experimental demonstration of a compact and high-performancelaser-pumped Rubidium gas-cell atomic frequency standard, IEEE Transactions onInstrumentation and Measurements, Vol. 55, No. 2, pp. 429-435, April (2006)
Laser-pumped Rb demonstrator (Neuchâtel)ESA-funded project
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 82 -
PP volume: 1.1 L
Overall volume: 2.4 L
Performance goal:
Stability of a Passive H Maser
(9·10-13·-1/2 demonstrated)
C. Affolderbach, R. Matthey, F. Gruet, G. Mileti, Realisation of a compact laser-pumped Rubidium frequencystandard with < 1x10-12 stability at 1 second, EFTF-2010
Stability results with LP-Rb clock
9x10-13 -1/2
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 83 -
-4 -2 0 2 4 6 80
50
100
150
200
250
300
350
400
450
Maximal slope : 600 Hz / GHz
Maximal slope : 420 Hz / GHz
Rub
idiu
m c
lock
fre
quen
cy [
Hz]
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
F=2
Total(F=1)+(F=2)
F=1
Ligh
t shi
ft (
10 -7
)
Laser wave length
(dfclock/dIlaser and dfclock/dflaser)
Light-shift
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 84 -
-4 -2 0 2 4 6 80
5
10
15
20
25
30
D2 lines of Rb87
F = 1F = 2
Pho
tocu
rren
t [mA
]
Laser diode frequency [GHz]
Laser diode frequency [GHz]g
0 2 4 6 8 103500
3505
3510
3515
3520
3525
(0,1 mW/ mm2)
(S = 90 mm2)
Fit : 3500,4 + 2,31 x I
Fit : 3500,3 + 2,45 x I
Laser tuned to F=1
Laser tuned to F=2
"Clo
ck"
Freq
uenc
y [H
z]
Photocurrent [m A]
15
-4 -2 0 2 4 6 80
50
100
150
200
250
300
350
400
450
Maximal slope : 600 Hz / GHz
Maximal slope : 420 Hz / GHz
Rub
idiu
m c
lock
fre
quen
cy [
Hz]
-1000 -800 -600 -400 -200 0 200 400 600 8000.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
10-8
Refer
ence
abs
orpt
ion
line
"10
MH
z" C
lock
freq
uen
cy (
-9'9
99'
996
) [H
z]
Light-shift (AC Stark effect)Shift of the resonance frequency induced by the optical radiation (I, )
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 85 -
-4 -2 0 2 4 6 80
5
10
15
20
25
30
D2 lines of Rb87
F = 1F = 2
Phot
ocur
rent
[mA
]
Laser diode frequency [GHz]
Laser diode frequency [GHz]1000 800 600 400 200 0 200 400 600 800"
Laser frequency detuning [MHz]
-200 -180 -160 -140 -120 -100 -80 -60 -40 -20 0 200.64
0.68
0.72
0.76
0.80
0.84
0.88
"zer
o li
gh
t-sh
ift"
lase
r fr
equ
en
cy
Rb
87 C
O 2
1-23
Rb
87
CO
22-
23
2·10-9
Reference saturated absorption
"10
MH
z" c
lock
freq
uen
cy (
-9'9
99'
996
) [H
z]
Laser frequency detuning [MHz]
Light-shift: some strategies to reduce it
2-zones 2-lasers with LIF
double-bulb Maser
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 86 -
S
P
example of pulse sequence (adapted from [10])
light
-wave
0.5 ms
0.2 ms
2.6 ms
pulseddouble-bulb Maser
See Godone et al., PRA 70 023409 (2004)
Pulsed Rb clock (INRIM-Torino)
AOMLaser
zL
HeterodyneDetector
Optical Signal
Microwave Cavity Cell
z
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 87 -
L
MicrowaveSynthesizer
RF Oscillator
= SwitchOCXO
Servo
A. Godone, S. Micalizio, C. E. Calosso, F. Levi, The pulsed Rb clock, IEEE Transactions on UFFC, Volume: 53 Issue:3 p. 525-529, (2006)
Light-shift suppression
(reducing dfclock/dIlaser and dfclock/dflaser)
by adding sidebands on the laser
shift unmodulated
Calculated light shift on F=1no mod.
laser frequencylight
shi
ft
M=2 4M=2 4
experimental result:
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 88 -
-2000 -1000 0 1000 2000
Clo
ck f
requ
en
cy
Laser carrier frequency detuning [MHz]
3·10-8
0modulated,
different intensities1 2-1 0 1 2-1 0
fmod = 400 MHz
Carrier detuning (GHz)
Ligh
t shi
ft
M=2.4M=2.45·10-85·10-8
C. Affolderbach, C. Andreeva, S. Cartaleva, T. Karaulanov, G. Mileti, D. Slavov, Light shift suppression in laseroptically-pumped vapour-cell atomic frequency standards, Applied Physics B, Volume 80, N. 7, (2005)
Drift, aging and environmental effects
7450
7500
7550
7600
30 W 11 W "no" light
reso
nanc
e sh
ift (
Hz)
3255
3256
3257
3258
ce s
hift
(Hz)
pure N2: 1.6·10-9 /K
buffer-gas mixture:
pure N
Example of the Rb standards
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 89 -
40 45 50 55 60 65
-1100
-1080
-1060
-1040
-1020
-1000
39 W 11 W "no" light
reso
nanc
e sh
ift (
Hz)
Cell temperature (°C)
7400
45 50 55 60 653252
3253
3254
reso
nan
c
Cell temperature (°C)
gas mix: < 6·10-11 /K
pure N2
pure Ar
long-term stability:
temperature within few mK
clock stability around 10-14
The role of the quartz oscillator and LO
Tra
nsm
itted
ligh
t
Microwave frequency
LO (quartz)
- Direct AM noise and FM AM noise
- Aliasing effects (Phase noise)
“Dick effect”
Example of the laser-pumped Rb clock
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 90 -
Dick effect
2/1
1
22 2
nmnnoisePMy nfSC
2222)()()()( ls
ynoisePM
ynoiseI
ytotaly
Finally:
See Deng et al., PRA 59 (1) 773 (1999)
See Mileti et al., IEEE J. of Q. Electr. 34 (2) 233 (1998)
16
10-12
RIN = 1 10-12
4.10-12
9.10-12
0 5
20 KHz/Hz0,5
50 KHz/Hz0,5
Slaser
= 100 KHz/Hz0,5
devi
atio
n y
-
1/2
Effect of laser AM and FM noise
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 91 -
1 2 3 4 5 6 7 8 9 10
10-13
4.10-14
9.10-14
2,5.10-13
RIN 1.10
5 KHz/Hz0,5
10 KHz/Hz0,5
Pred
icte
d A
llan
d
DC Photocurrent [A]
2. CPT cell and chip-scale standards
S
P
Coherent Population Trapping“dark” state
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 92 -
Potential advantages of using CPT:
• No microwave cavity
• Reduced light-shift
Open issues: 2-colours coherent laser source, signal contrast
Examples of past or on-going developments
• Rubidium CPT Maser (INRIM)
F. Levi et al., Realization of a CPT Rb maser prototype for Galileo, FCS-EFTF 2003
• Pulsed Cs CPT standard (SYRTE)
N. Castagna et al., Investigations on continuous and pulsed interrogation for a CPT atomic
clock, IEEE Trans UFFC, 2009 Feb;56(2):246-53.
• CW Rubidium CPT standard with
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 93 -
• CW Rubidium CPT standard with
buffer-gas or wall-coating (LTF-UniNe)
E. Breschi, G. Kazakov, R. Lammegger, B. Matisov,L. Windholz, and G. Mileti, Influence of LaserSources with Different Spectral Properties on theperformance of Vapor Cell Atomic Clocks Basedon lin lin CPT, IEEE Transactions on UFFC,V. 56, N. 5, p. 926, May (2009)
LTF CPT standard using a Rb wall-coated cell (ASRH-FNS)
Example of research on CPT
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 94 -
Example of recent research on CPT
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 95 -
Towards chip-scale atomic clocks
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 96 -
Stable referenceSee Knappe et al., Appl. Phys. Lett., 85, (9), 2004
17
MEMS technology in Time & Frequency
• Need of low-consumption, low-weight and low-cost T&F devices
Example: GNSS receivers able to lock on PRN signals
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 97 -
• Key MEMS-based building blocks:
– Resonators
– Filters
– Oscillators
– Chip-scale atomic clocks
Physical principle and processes
o Magnetic resonance scheme, large number of collisions, etc.
Laser source (photons)
o Stable wavelength, narrow spectrum, ~ 100 W, low noise, etc.
Atomic vapour cell (atoms)
o Sealed, stable and reliable “container” of alkali atoms (~ 10 mm3)
Main building blocks for a chip-scale atomic clock:
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 98 -
Control electronics
o Low consumption thermostat, locking, etc. (~ 10 mW)
Local oscillator
o Low consumption and low phase noise microwave source
Example of clock specifications: 30 mW, 10-11 @ 1000s, 1 cm3
Examples of application: replace quartz oscillators
Examples of US prototypes
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 99 -
mUSO projectESA-funded project, collaboration between Spectratime SA, LTF-UNINE and EPFL (ESPLAB, SAMLAB)
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 100 -
C. Schori, G. Mileti, B. Leuenberger, P. Rochat, CPT Atomic Clock based on Rubidium 85, EFTF-2010.
Other Swiss and European on-going research:
• Cs CPT chip-scale atomic clock
D. Miletic, C. Affolderbach, E. Breschi, C. Schori, Christian, G. Mileti, M.
Hasegawa, Madoka, R. Chutani, Ravinder, P. Dziuban, R. Boudot,
Rodolphe, V. Giordano, C. Gorecki, Fabrication and spectroscopy of Cs
vapour cells with buffer gas for miniature atomic clock, EFTF-2010
• Wall-coating and CPT and double-resonance
E. Breschi, G. Mileti, Dark resonance in wall-coated cell for Rb-clocks, EFTF-2010
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 101 -
E. Breschi, G. Mileti, Relaxation of HF-ground state coherence of Rb atoms contained
in wall-coated cell, The 19th International Conference on Laser Spectroscopy (ICOLS
2009), Hokkaido (Japan), 7-13 June (2009)
T. Bandi, C. Affolderbach, G. Mileti, Study of Rb00 hyperfine double resonance
transition in a wall coated cell, EFTF-2010
• Chip-scale double-resonance
Miniature atomic clock and quantum sensors, SNF-Sinergia project, LTF-EPFL (SAMLAB,
LMTS, LEMA, LPM) collaboration
REFERENCE CELL
ATOMIC RESONATOREOM
BEAM SPLITTER
www.mac-tfc.eu
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 102 -
FIBER COUPLER
DFB
18
Miniature atomic vapor cells and applications
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 103 -
Neuchâtel miniature atomic vapor cells (LTF-SAMLAB)
Dia=5 mm
L =10x10 mm 200 - 500 um
500-2000 um
Silicon wafer
Photolithography and cavity etching by DRIE
Wafer-level anodic bonding of Si with glass
Dicing
200 - 500 um
Rb deposition
Dia=5 mm
L =10x10 mm 200 - 500 um
500-2000 um
Silicon wafer
Photolithography and cavity etching by DRIE
Wafer-level anodic bonding of Si with glass
Dicing
200 - 500 um
Rb deposition
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 104 -
Cell closing / Anodic bonding of glass lidCell closing / Anodic bonding of glass lid
Y. Pétremand, R. Strässle, D. Briand, C.Schori, G. Mileti, P.Thomann and N. de Rooij, Low Temperature Indium-based Sealing of Microfabricated Alkali Cells for ChipScale Atomic Clocks, EFTF-2010
Besançon miniature atomic vapor cells (UFC-FEMTO)
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 105 -
Potential applications:
• Chip-scale frequency references
• Chip-scale atomic clocks (microwave
and optical)
• Chip-scale atomic magnetometers
Miniature alkali vapour cells
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 106 -
University of
Neuchâtel (LTF)
and EPFL (IMT-
SAMLAB)
• Chip-scale gyroscopes
In the future:
• Atom chips
• Quantum computing
• Quantum communication
Miniature wavelength reference
Demonstrated
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 107 -
J. Di Francesco, F. Gruet, C. Schori, C. Affolderbach, R. Matthey, G. Mileti, Y. Salvadé, Y.Petremand, N. de Rooij, Evaluation of the stability of a VCSEL stabilised to a micro-fabricated Rubidium vapour cell, Photonics Europe 2010
0.0
0.2
0.4
0.6
0.8
1.0
85Rb, F=3
tcell
=60°C
tcell
=82°C
tcell
=110°C
No
rmal
ized
Tra
nsm
issi
on
Laser Frequency
85Rb, F=2
)000'1001(
910
ss
y
stability:
Summary and conclusions (cell standards)
• Rb/Cs vapor frequency standards constitute a well
established technology which used in every day life
applications (telecoms, GNSS, instrumentation, etc.)
• They also a very active field of scientific research, along
three main directions:
3ème cycle de la physique en Suisse Romande, Atomic clocks and fundamental tests in PhysicsG. Mileti, Introduction and vapour cell standards, 25.02.2010 - 108 -
Studying the atoms-photons resonant interaction;
Developing improved atomic clocks;
Miniaturization (reduction of power and prize)
• Key basic technologies:
Laser sources, vapor-cells, microwave source and cavity
top related