From Dancing WavePacket to the Frictionless Atom Cooling 11/

Transcription

1 From Dancing WavePacket to the Frictionless Atom Cooling 11/

2 outline Motivation Quantum friction and the classical picture The frictionless atom cooling

3 Initial problem: v v e ω(t) = 2 ml 2 (t) L(t) =L 0 + vt v e 1 ml v v e : ADIABATIC APPROXIMATION. v v e : SUDDEN APPROXIMATION. v v e :?

4 Simulation Method For a linear expansion or contraction potential, the wavefunction will be M. V. Berry & G. Klein, J. Phy. A 17, 1805(1984), C. H. Chang, personal note. AND ϕ n ( x L(t) ) E n (t) THE INSTANTS WAVEFUNCTION, THE INSTANTS ENERGY.

5 Simulation Result I: adiabatic limit Set v e =1/mL 0, v = v e / E/E L/L 0 E(t) ω(t) ω 0 E 0

6 Simulation Result II: sudden limit v = 10v e 15 E/E L/L 0 E(t) E m( ω 2 t ω 2 0) Ψ0 x 2 Ψ 0.

7 Simulation Result III v =0.5v e 10 8 E/E L/L (E E ad )/E L/L 0

8 Simulation Result III v =0.5v e 10 8 E/E L/L (E E ad )/E 0 Why the wavepacket distribution and energy oscillate 0.1 during the contraction? L/L 0

9 Simulation Result III v =0.5v e ψ 0 = a 0 φ 0 + a 2 φ E/E L/L 0

10 Quantum Breathing Breathing oscillation induced by sudden change A. Minguzzi & D. M. Gangardt, Phys. Rev. Lett. 94, (2005). ω 0 ω 1 T = π/ω 1

11 Quantum Breathing: Experimental Result J. F. Schaff et al., Phys. Rev. A 82, (2010). shortcut decompression

12 Quantum Breathing: Experimental Result J. F. Schaff et al., Phys. Rev. A 82, (2010). induced by trap center shifting!! Avoid quantum breathing can enhance cooling efficiency!!

13 Analytical analysis: Method of time dependent eigenvectors For M. A. Lohe, J. Phy. A 42, (2009), C. H. Chang & T. M. Hong, in preparation (2010). The time-dep eigenvector is with b(t)=l(t)/l(0).

14 Analytical analysis: The energy change for packet in the time-dep trap I C. H. Chang & T. M. Hong, in preparation (2010). ψ 0 initial wavepacket projection operator evolution operator

15 Analytical analysis: The energy change for packet in the time-dep trap II The energy contributed from 1. Instaneous energy for trap ω(t) C. H. Chang & T. M. Hong, in preparation (2010). 2. The kinetic energy 3. The quantum friction T. Feldmann & R. Kosloff, Phys. Rev. E, 61, 4774(2000), R. Kosloff & T. Feldmann, Phys. Rev. E, 65, (2002). ḃ {ˆx, ˆp} [Ĥ(0), Ĥ(t)] 2b

16 Analytical analysis: The energy change for packet in the time-dep trap II The energy contributed from 1. Instaneous energy for trap ω(t) C. H. Chang & T. M. Hong, in preparation (2010). 2. The kinetic energy 3. The quantum friction ḃ {ˆx, ˆp} [Ĥ(0), Ĥ(t)] 2b T. Feldmann & R. Kosloff, Phys. Rev. E, 61, 4774(2000), R. Kosloff & T. Feldmann, Phys. Rev. E, 65, (2002). The energy depend on the packet follows or resists to the trap motion!!

17 Analytical analysis: The energy change for packet in the time-dep trap III C. H. Chang & T. M. Hong, in preparation (2010). with

18 Analytical analysis: The energy change for packet in the time-dep trap III C. H. Chang & T. M. Hong, in preparation (2010). with

19 Analytical analysis: The energy change for packet in the time-dep trap III C. H. Chang & T. M. Hong, in preparation (2010). with Quantum breathing term

20 Quantum breathing during the contraction C. H. Chang & T. M. Hong, in preparation (2010). The period is determined by

21 Corresponding effect in classical field C. H. Chang & T. M. Hong, in preparation (2010). The harmonic trap can be constructed by electromagnetic field The electron in the classical field A = 1 B( y, x, 0), 2 Ĥ = ˆp2 x +ˆp 2 y 2m + e2 B 2 8mc 2 (x2 + y 2 )+Ĥz We chose eb c =2mω = 4 L 2 (t), E = 1 c A t, B = A,

22 Why the packet dancing in the time-dependent harmonic trap C. H. Chang & T. M. Hong, in preparation (2010). The oscillation appear as the projecting from the initial state to the eigenvectors. The harmonic trap decide the breathing frequency induced by the quantum friction. The quantum breathing modify the energy from the friction term in the trap.

23 Conclusion I The general solution which include sudden and adiabatic approximation is found. The quantum breathing will modify the energy in the time-dep trap.

24 PartII Frictionless Cooling in the timedependent harmonic trap

25 Fast Optimal Cooling between two states P. Salaman et al., Phys. Chem. Chem. Phys. 11, 1027(2009). Xi Chen et al., Phys. Rev. Lett. 80, (2009). J. F. Schaff et al., Phys. Rev. A 82, (2010).

26 Frictionless Cooling in the trap Our Strategy The energy change equivalent to the adiabatic result: E f = ω f ω 0 E 0

27 Frictionless Cooling in the trap Our Strategy II C. H. Chang & T. M. Hong, in preparation (2010). Besides the original condition: We add conditions to avoid Quantum Breathing & Kinetic Energy!!