Fundamental physics with diatomic molecules
D. DeMille
CP-violation
quantum computation
hadronic weak interactions
quantum phase transitions(?)
Graduate Students:Frederik Bay, Sarah Bickman, Yong Jiang
Postdoc:Dave Kawall
Undergrads:Yulia Gurevich, Cliff Cheung
Funding: Research Corporation, Packard Foundation, NSF, NIST, Sloan Foundation, CRDF
Search for the Electron Electric Dipole Moment
T-violation: a window to new physics
•CP-violation observed in K- and B-mesons ⇒ T is NOT conserved in nature
• Observations consistent with standard model description (CKM)but also consistent with other explanations
• CP-violation in SM is minimal: extensions to SM almost inevitably include NEW sources of T-violation
• Observed baryon asymmetry in universe REQUIRES new sources of T-violation
An EDM Violates P and T B-B rrrr ⋅σµ=⋅µ−=dipoleMagneticH E- E- rrrr⋅σ=⋅= ddH dipoleElectric
CPT theorem ⇒ T-violation = CP-violation
P T
How does an electron EDM arise?not renormalizable⇒ loop diagrams
2 5 µνµνψσγψ Fde
d =L
γ
eeExperimental limit: |de| < 1.6×10-27 e⋅cm
~10-29 e·cmTechnicolor10-27-10-28 e·cmMulti-Higgs10-26-10-29 e·cmLepton flavor-changing10-26-10-28 e·cmLeft-right symmetric
< 10-25 e·cmSupersymmetry~10-41 e·cmStandard Model
Predicted |de|CP-violation model
de is a powerful probe for new physics!
General method to detect an EDM:
B
ω=2µΒ
ω=2µΒ
E
+2dE
+2dE
E
-2dE
-2dE
Energy level picture:
Figure of merit for statistical sensitivity:
( )( )NTE
NSTE
resolutionshift &⋅⋅=∝ −1//1
Selective excitation and laser-induced alignment of an Ω-doublet level:
1+1-
~12 MHz
X(0) [1Σ+]
0+
1-
2+
~10 GHz
•••
a(1) [3Σ+]
2+2-
•••
Laser pulseλ ~ 571 nm
bandwidth ~ 1 GHz ~ ∆νDoppler
m = +1m = -1m = 0
linear polarization ε ⊥ B⇒ |f> = |+1> + |-1> = |↔>
Zeeman splitting0-300 kHz typical
Present Experimental Setup
Pulsed Laser Beam5-40 mJ @ 100 Hz ∆ν ~ 1 GHz ε ⊥ B
Larmor Precessionν ~ 100 kHzPhoto-
multiplier tube B
solid quartz lightpipes
DataProcessing
Vacuum chamber
0
10
20
30
40
50
0 50 100 150 200time from laser pulse (µs)
Sign
al (m
V)
Noise consistentwith shot noise on
background
FFT Power Spectra of Signal-Exponential Fit
0
0
0
0
0
0
100 150 200 250 300 350 400Beat frequency (KHz)
Arb
. Uni
ts
~10 s integration
Observation of quantum beats in PbO
Signals at two different values of magnetic field B
Searching for Supersymmetrywith the electron EDM
Implications of current and ongoing electron EDM searches
HsFA-CP
A-UnAlign
de (e⋅ cm)10-26 10-28 10-30 10-32 10-34
NAIVE SUSY
SO(10) GUT
AC: Accidental CancellationsHsF: Heavy sFermionsA-CP: Approx. CPA-Un: Approx UniversalityAlign: AlignmentE-Un: Exact Universality
AC E-Un
The PbO EDM group
Funding: NSF ITR, Packard Foundation, Keck Foundation
Quantum computation withtrapped polar molecules
Graduate Students:Sunil Sainis, Jeremy Sage, Marco Ascoli
Postdoc:Jamie Kerman
Undergrad:Peter Gilbert
What is a quantum computer?
Register = collection of individually addressable 2-level systems
Processor = Controllable, time-dependent Hamiltonian
Any logical operation = 1-bit rotations (0a↔1a)
+ CNOT: (0a↔1a iff xb=1)
Q: So What?
A: Quantum algorithms using superpositions and entanglement
make certain problems (e.g. factoring, eigenvalues/vectors, etc.)
computationally tractablebecause of exponential speedup
CNOT requires bit-bit interactions
Without interactions:
Desired:a flips if b=1
|0>a|0>b
|1>a|0>b
|0>a|1>b
|1>a|1>b
Undesired:a flips if b=0
CNOT requires bit-bit interactions
With interaction H' = aSa⋅Sb
|0>a|0>b
|1>a|0>b
|0>a|1>b
|1>a|1>b
THIS IS A TWO-BIT QUANTUM COMPUTER!
Size of interaction term “a”determines maximum gate speed:
τ-1 ~ ∆ν ~ a
Issues for quantum computation
• Speed:how fast can you manipulate bits?
(Determined by size of bit-bit coupling)
• Decoherence & Fidelity:how many logical operations
can you perform before quantum state is destroyed?
(Determined by coupling of bits to outside world + degree of control over gate operations)
• Scaling up:how many bits can you store and manipulate?
(Determined by technical details)
H0 = -d⋅E, Ea ≠Eb; H' = -da⋅db/r3
distance between bits "r" isfixed in optical trap:
-V
+V
Standing-wave trap laser beam
Strong E-field
Weak E-field
E-field due to eachdipole influences
its neighbors
Our goal: a quantum computerwith bits = polar molecules
• Polar molecules in optical lattice trap• bits = “permanent” electric dipole moments of
polarized diatomic molecules• interaction = electric dipole-dipole
(fairly strong, a ~ 3-30 kHz)• processor = rf electric resonance (easy, like NMR)• addressing = spectroscopic, with E-field gradient• decoherence = Raman scattering from trap laser
(T ~ 5 s; Nop ~ 105 !)• readout = laser-induced ionization + imaging
(easy, but destructive)• scaling up? ( 104 bits looks reasonable!)
Technologically interesting thresholds:
Nop 104 ⇒ robust error correction OK?
Crude scaling ⇒ 300 bits, 104 ops/s = equivalent of teraflop classical computer
Why use polar molecules for quantum computation?
How to make them?Photoassociation:
(Use photon to carry away excess energy)
s1+p2=A
s1+s2= X
photo-association
laserspont. emission to high vib. level
excited-state potential
ground state potential
Internuclear Distance R
Ener
gy
stimulated Raman transfer to ground state (2 lasers)
Molecules formed at same translationaltemperature as atoms (+1-2 photon recoils)
Minimal decoherence⇒ weak trap ⇒ ultracold molecules
JeremySage
SunilSainis
JamieKerman
MarcoAscoli
Research opportunities in the DeMille group
Electron EDM: 1 student
quantum computation: 1 student(?)
hadronic weak interactions (NEW): 1-2 students
direct cooling of polar molecules (NEW):1-2 students
Dave DeMilleOffice: 46 SPL; Labs 23 & 28 SPL
Many-body physics w/ultracold polar molecules
New quantum phases:K Goral et al., Phys. Rev. Lett. 88, 170406 (2002):
“Quantum Phases of Dipolar Bosons in Optical Lattices”
Tunable strength and isotropy:S. Giovanazzi, A. Goerlitz, and T. Pfau, Phys. Rev. Lett. 89, 130401 (2002):
“Tuning the Dipolar Interaction in Quantum Gases”
BCS pairing:M. Baranov, et al., Phys. Rev. A 66, 013606 (2002):“Superfluid pairing in a polarized dipolar Fermi gas”
Controlled chemical reactions:N. Balakrishnan and A. Dalgarno, Chem. Phys. Lett. 341, 652 (2001):
“Chemistry at ultracold temperatures”
Strong, long-range, anisotropic, tunable interactionsat ultracold temperatures--a new regime
Axial hadronic weak interactions
VN, AN
Ve, Ae
Z0
N = p, n
e
VeAN and AeVNterms violate parity
VeAN couplings small, barely known,
sensitive to new physics such as
quark substructure
~10% left-right asymmetry in molecules!!
γ
N
e
Z0, W±
Intra-nuclear parity-violating weak
interactions create nuclear “anapole
moment” that couples magnetically
to electron