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© Kungl. Vetenskapsakademien
Serge Haroche Collège de France and École Normale Supérieure, Paris, France
The Nobel Prize in Physics 2012
David J. Wineland National Institute of Standards and Technology (NIST) and University of Colorado Boulder, CO, USA
“For ground-breaking experimental methods that enable measuring and
manipulation of individual quantum systems.”
“We never experiment with just one electron or atom or (small) molecule. In thought-experiments we sometimes assume that we do; this invariably entails ridiculous consequences…”. 1952 E. Schrödinger
Experiment with single atoms (ions) and with one or few photons
Ion in a trap Photon in a cavity
Manipulation and observation with photons
Manipulation och observation with atoms
A two-level system is coupled to a quantized harmonic oscillator
n=50
n=51
1. Methods Background New techniques
2. Applications Within science For the future For today
Capturing and cooling an ion
Ion trap technique 1970s Paul and Dehmelt, Nobel prize 1989 Doppler cooling (with laser light) proposed by Wineland and Dehmelt for ions 1975 demonstrated experimentally for ions 1978 Chu, Phillips, Cohen-Tannoudji, Nobel prize 1997
Ion traps
An ion trap Linear Paul trap Electric field + Radio frequency field
NIST home page
Electrodes
Lasers Ions
Observation of ions
Hg+
5d106s2 2S1/2
5d106s 6p 2P1/2
5d96s2 2D1/2
Wineland’s and Toschek’s groups 1986
forbidden
Be+
2S1/2 F=2,mF=2
2P3/2 F=3,mF=3
NIST home page
Sideband cooling
v=0 v=1 v=2
v=0 v=1 v=2 ωv
ω0
|↑>
|↓>
Quantized motion
Wineland’s group 1989 (1D) och 1995 (3D)
Cooling in the lowest energy state of the trap Control of the internal and external states of the ion
ω0−
ωv
|ϕ0>=|↓> |0>
|ϕ1>= (α|↓> +β|↑>) |0> Superposition of internal states
|ϕ2>= α|↓>|0>+β|↓>|1> =|↓> (α|0>+β|1>)
|↑>|0> →|↓> |1>
Control of the state of an ion
Red sideband π pulse
Superposition of vibrational states
Cirac , Zoller, theory,1995 Wineland’s group, experiment 1995 Blatt’s group, experiment for two ions 2003
v=0 v=1
v=0 v=1 |↑>
|↓>
ω0−
ωv
Cavity Quantum Electrodynamics (CQED)
Properties of one atom in a cavity Kleppner , Walther, Haroche (1985) CQED in the optical domain: Kimble Circuit QED: using supraconducting circuits
Capture of microwave photons
Supraconducting mirrors in niobium 0,8K
39 000 km
Q=4x 1010 Tc= 130 ms 51,1 GHz
Microwave photons
ENS home page
A half cavity
Rb, n=50
n=51 51 GHz
Circular Rydberg atom l=|m|=49
Experiment with photons
B: Preparation of Rydberg atoms R1, R2: Resonant cavities where superpositions of ↑ and ↓are created D: Field ionisation detector R1, R2, D: Ramsey interferometer C: Cavity
Measurement of 0 or 1 photon
|↓>
y
x z |↑>
|↑> +|↓>
|↑> +eiφ|↓>
|↑>
|↓>
y
x z |↑>
|↑> +|↓>
|↑> +|↓>
|↑>
0 photon φ=0
|↓>
Measurement of 0 or 1 photon
Haroche’s group, 1990, 1999, 2007
|↓>
y
x z |↑>
|↑> +|↓>
|↑> -|↓>
|↑>
1 photon φ=π
|↑> >
Phase shift
Measurement of 0 or 1 photon
Many atoms see the same photon
time (s)
|↓>
|↑>
|↑>
|↓>
Measurement of 0 or 1 photon
Measurement of a few photons
Quantum feedback (2011)
Observation of the progressive collapse of a wave function
1. Methods Background New techniques
2. Applications Within science For the future For today
Schrödinger’s cat
1935 Schrödinger Difficult to apply quantum mechanics to everyday’s life! When does a superposition of states stop to exist and become one state or the other? Transition between the quantum and classical worlds
|ϕ1>= |↑>|αe-iφ> +eiφ|↓>|αeiφ>
|ϕ0>= (|↓> + |↑>) |α> α Coherent field
Decoherence of Schrödinger’s cat
Haroche’s group 1996 Wineland’s group 1996
Entanglement between the atom and the field
Decay of coherence
After the cavity:
Dead cat Living cat
”Film” of the decoherence of a Schrödinger’s cat
Wigner function
Superposition Statistical mixture
Towards quantum computers
Bits 0 1 Quantum bits
|0>
y
x z |1>
Many systems proposed for quantum computers: Ions in a trap (14 qubits) Atoms in a cavity Superconducting circuits Atoms in optical lattices etc
N qubits: superposition of 2N states Parallelism interesting for some operations
First 2qubit quantum gate CNOT operation Wineland’s group 1995
Optical Clocks
Caesium atom
Precision of an optical ion clock 10-17
Aluminium ion
Microwave Visible
104
Optical clocks using quantum logic
27Al+
1S0
3P1
Quantum logic spectroscopy technique Al-Be
1.12 PHz 8 mHz bandwidth
No strong transition for cooling and detection
Be+ 2S1/2
F=2,mF=2 F=1,mF=1
2P3/2
F=3,mF=3
Cooling och detection
Quantum logic
Wineland’s group 2005
How does one measure the precision of optical clocks?
Frequency comb technique: Hall and Hänsch 1999 NP:2005
Optical ion clocks
Mg+
8 x10-18
Wineland’s group 2010
Al+
Difference in height 30 cm
Difference in velocity: a few m/s
Serge Haroche Collège de France and École Normale Supérieure, Paris, France
The Nobel Prize in Physics 2012
David J. Wineland National Institute of Standards and Technology (NIST) and University of Colorado Boulder, CO, USA
“For ground-breaking experimental methods that enable measuring and
manipulation of individual quantum systems.”
