Ultracold molecules - a new frontier for quantum & chemical physics Debbie Jin Jun Ye JILA, NIST & CU, Boulder University of Virginia April 24, 2015 NIST, NSF, AFOSR, ARO
Ultracold atomic matter Precise control of a quantum system The most precise measurements, e.g., clock Quantum information Quantum sensors Control: A tool for understanding complexity Strongly correlated many-body quantum systems Superfluidity & Superconductivity Control atomic interactions Regulate atomic motions Quantum magnetism Quantum chemistry
Atomic Interactions Short-range collisions 0 interaction strength We can understand & control them!
Quantum gas of polar molecules Extend capability to control complex quantum systems Study frontier problems in strongly correlated quantum material, with well-understood microscopics tunable, long-range interactions non-equilibrium quantum dynamics Quantum metrology, E Exotic quantum matter Correlated material, Chemistry
energy Ultracold molecules: The challenge KRb two atoms E/k B =6000 K molecule
energy Ultracold molecules: The challenge Molecules are complex! two atoms vibration 100 K molecule
energy Ultracold molecules: The challenge Molecules are complex! rotation 0.1 K
energy Ultracold molecules: The challenge Molecules are complex!
energy Ultracold molecules: The challenge Molecules are complex! nuclear spin 38 mk
log 10 (density [cm -3 ]) Technology for making cold molecules Carr, DeMille, Krems, Ye, New. J. Phys. 2009. Quantum gas of molecules 12 Towards quantum regime 9 6 3 Laser cooling Evaporative cooling Sympathetic cooling Photo-association Stark, magnetic, optical deceleration -9-6 -3 0 Buffer-gas cooling High resolution collisions/reactions Precision test log 10 (T [K])
energy Associate ultracold atoms into molecules two atoms 6000 K molecule
Make Feshbach molecules Energy V(R) R R R R E binding Large, floppy molecules 0 Interaction tuned by scattering resonance 40 K 87 Rb Magnetic field B > Scattering length a Magnetic field B
energy Weakly bound molecules no dipole moment losses 6000 K
Coherent two-photon transfer the absolute ground state (entropy-less chemistry) Fully coherent, >90% efficiency 690 nm 970 nm Laser 1 Laser 2 frequency 6000 K Beat note 125 THz 36 nuclear spin states: We populate & control single state S. Ospelkaus et al., Phys. Rev. Lett. 104, 030402 (2010).
Polar molecules in the quantum regime Temperature ~ 100 nk Density ~10 12 /cm 3 T/T F ~ 1.3 40 K Fermions 87 Rb Bosons K.-K. Ni et al., Science 322, 231 (2008). KRb molecules (Dipole ~0.5 Debye)
Density (10 12 cm -3 ) Chemistry near absolute zero Trapped molecules in the lowest energy state (electronic, vibrational, rotational, hyperfine) Two-body loss n( t) n( t) 2 T = 200 nk > 1 s lifetime Time (s) KRb + KRb K 2 + Rb 2
Cold collisions between identical Fermions (1) Particles behave like waves (2) Angular momentum is quantized s p d 0 1ħ 2ħ (3) Quantum statistics matter 0 1 1 0 Fermions c L = 1, p-wave collisions
Energy Ultracold chemistry Ospelkaus et al., Science 327, 853 (2010). At low T, the quantum statistics of fermionic molecules suppresses chemical reaction! debroglie wavelength Rate proportional to T distance between the molecules
Energy Ultracold chemistry Ospelkaus et al., Science 327, 853 (2010). Distinguishable molecules do not enjoy the suppression rate is x 100 higher! debroglie wavelength distance between the molecules
Anisotropic dipolar collisions K.-K. Ni et al., Nature 464, 1324 (2010). p-wave barrier m L = +1, -1 m L = 0 Collisions under a single partial wave (L = 1 ).
2D geometry loss suppression D (cm 3 s -1 ) 10-9 3D D 10-10 10-11 10-12 0.00 0.05 0.10 0.15 0.20 Dipole moment (D) Theory: Büchler, Zoller, Bohn, Julienne M. de Miranda, et al., Controlling the quantum stereodynamics of ultracold bimolecular reactions, Nature Phys. 7, 502 (2011). E
3D optical lattice suppressing chemical reaction with quantum Zeno effect Lifetime ~ 20 s Filling ~ 5% τ = 25(2) seconds A. Chotia et al., Phys. Rev. Lett. 108, 080405 (2012). B. Zhu et al., Phys. Rev. Lett. 112, 070404 (2014).
Spin exchange in a lattice of molecules Barnett et al., Phys. Rev. Lett. 96, 190401 (2006). Micheli et al., Nature Phys. 2, 341 (2006). Gorshkov et al., Phys. Rev. Lett. 107, 115301 (2011). Rotation Spin Long-range dipolar interactions for direct (~khz) spin exchanges - motion & spin decoupled Fully tunable with electromagnetic fields Dipole moment 270 khz 70 khz 2.23 GHz
A good system to study many-body quantum localization? D. Huse, G. Shlyapnikov, M. Lukin, E. Demler, Molecules (material) are physically pinned down, but spins (excitations) can be exchanged and mobile! Energy flow in a macro-molecule!
Interaction strength for quantum magnetism Flip-flop term The oscillation frequency for a pair of molecules is J /2h.
Number (10 3 ) A Dipolar Spin-Lattice Model B. Yan et al., Nature 501, 521 (2013). N=1 > N=0> Start with N=0. Drive a coherent spin superposition. 1 2 Probe spin coherence at T. (Ramsey spectroscopy)
Coherent time Contrast Oscillations due to dipolar interactions 1.0 0.8 N=1.77x10 4 N=5x10 3 0.6 0.4 0.2 1/N scaling 0.0 0 20 40 60 80 100 T (ms) 1, 1 0, 0 1, 0 0, 0 Oscillation frequencies & decay time both depend on rotational states
Contrast Contrast Control dipolar interaction K. Hazzard et al., Phys. Rev. Lett. 113, 195302 (2014). 1,-1 1,0 0,0 1,1 1 0.5 0 1 Theory (MACE) Dark squares: 0,0> -> 1,0> Red circles: 0,0> -> 1,-1> (time rescaled by ½). 1,-1 Experiment 1,-1 f = 106 Hz, f/ 2, f/2 1,0 1,0 0.5 J 2 ~ 102 Hz 0 for 0,0> to 1,0> ( J 2 ~ 51 Hz for 0,0> to 1,-1>) One fitting parameter (filling 5-10%) reproduces the experiment
Highly filled optical lattice ~5% filling in a 3D lattice Goal: A near zero entropy 3D lattice
Creating molecules in a 3D lattice 1. Rb MOTT insulator 2. Add lots of K atoms (tune Rb K interaction energy) 3. Magnetic association & Raman transfer
Rb Mott insulator imaged in-situ A superfluid BEC phase transition to a MOTT insulator filling Lattice depth 12 E rec 18 E rec 24 E rec 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 1 10 100 Rb (10 3 ) 2000 Rb 50,000 Rb
Imaging of K in momentum & real space Peak Filling Fraction 1.0 K Filling vs Number 0.9 0.8 0.7 0.6 0.5 0.4 10 4 10 5 K Number
Rb filling Rb Overlap of Rb and K K Rb & K overlap 1.4 1.2 1.0 5000 Rb 10 5 K Vary a KRb before loading lattice 0.8 At a KRb = 0, Rb MI unaffected by K 0.6 0.4 0.2 0.0-300 -200-100 0 100 200 a K-Rb (a 0 )
Pairing up K-Rb in lattice without heating Load the lattice at a KRB = 0 Jumping across the resonance dilutes the filling (populating higher bands) Flip to a noninteracting spin state ( 9/2,-7/2>) to avoid resonance when ramping B Flip back to 9/2,-9/2>, then proceed with Feshbach association B K: F =9/2,m F = 9/2> + Rb: F =1,m F =1>
KRb Feshbach / Rb A low entropy lattice of molecules Convert > 60% of Rb MOTT Insulator to KRb Image of KRb For BEC of a few 10 3 Rb, the peak filling of Rb ~ 1 0.8 0.6 To measure KRb, dissociate the molecules & count the numbers of K = Rb 0.4 0.2 0.0 0.1 1 10 Rb (10 4 ) Ground state KRb, ~ 40% filling in 3D lattice (entropy/molecule ~ 1.7 k B ) ~5% filling
Special Thanks (KRb team): Bo Yan Steven Moses Bryce Gadway Jacob Covey Former members: Brian Neyenhuis Amodsen Chotia Marcio de Miranda Dajun Wang Silke Ospelkaus Kang-Kuen Ni Avi Pe er Josh Zirbel Theory collaborations: J. L. Bohn, K. Hazzard, P. S. Julienne, S. Kotochigova, M. Lukin, A. M. Rey, P. Zoller