Metastability and thermalization in Bose-Hubbard circuits Doron Cohen, Ben-Gurion University Circuits with condensed bosons are the building blocks for quantum Atomtronics. Such circuits will be used as QUBITs (for quantum computation) or as SQUIDs (for sensing of acceleration or gravitation). We study the feasibility and the design considerations for devices that are described by the Bose-Hubbard Hamiltonian. It is essential to realize that the theory involves “Quantum chaos” considerations. • The Bose-Hubbard Hamiltonian. • Relevance of chaos for Metastability and Ergodicity. • Thermalization and quantum localization. Bosonic Junction STIRAP through chaos
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Metastability and thermalization in Bose-Hubbard circuits
Doron Cohen, Ben-Gurion University
Circuits with condensed bosons are the building blocks for quantumAtomtronics. Such circuits will be used as QUBITs (for quantumcomputation) or as SQUIDs (for sensing of acceleration or gravitation).We study the feasibility and the design considerations for devices thatare described by the Bose-Hubbard Hamiltonian. It is essential torealize that the theory involves “Quantum chaos” considerations.
• The Bose-Hubbard Hamiltonian.
• Relevance of chaos for Metastability and Ergodicity.
• Thermalization and quantum localization.
Bosonic Junction
STIRAP through chaos
The Bose Hubbard Hamiltonian
The system consists of N bosons in M sites. Later we add a gauge-field Φ.
Dittrich, Spectral statistics for 1D disordered systems [Phys Rep 1996];
DC, Periodic Orbits Breaktime and Localization [JPA 1998].
Manifestation of localization in thermalization?
∂f(ε)
∂t=
∂
∂ε
(g(ε)D(ε)
∂
∂ε
(1
g(ε)f(ε)
))g(ε) - local density of states
Rate of energy transfer [FPE version]:
A(ε) = ∂εD + (β1 − β2)D
For canonical preparation:
〈A(ε)〉 =
(1
T1−
1
T2
)〈D(ε)〉
subsystem 1 subsystem 2
A
Here we considered a Bose-Hubbard system
where the diffusion is in x
x = the occupation of subsystem 1
N−x = the occupation of subsystem 2
Hurowitz, DC (EPL 2011) - MEQ version
Tikhonenkov, Vardi, Anglin, DC (PRL 2013)] - FPE version
Bunin, Kafri (JPA 2013) - NFT version
Khripkov, Vardi, DC (NJP 2015) - Resistor network calculation of D(ε)
Question: Do we have ξ = g(ε)D(ε) ?
Phase space formulation of the QCC condition
We propose a generalized QCC condition for the purpose of breaktime determination:
Rough version: t <
[Ωclt
ΩE
]tH
Refined version: N sct < Fqm
erg
[NEΩE
]Ωclt
NE = total number of states within the energy shell (r0 dependent)
Fqmerg = filling fraction for a quantum ergodic state, say = 1/3
ΩE = number of cells that intersect an energy-surface
Ωclt = explored phase-space volume during time t (starting at r0)
N sct ≈ t/tE = semiclassical number of participating-states during time t
phase−space cells
E−surfaces
|〈rj|Eα〉|2
It is unavoidable to use in the semiclassical analysis
improper Planck cells. Namely, a chaotic eigenstate is
represented by a microcanonical energy-shell of thick-
ness ∝ ~d and radius ∝ ~0. For some preparations it
is implied that NE ΩE rather than NE ∼ ΩE .
Cartoon: ΩE = 8, while NE = 5.
Proper Planck cell: ∆Q∆P > ~/2 for each coordinate.
The ”quantum exploration” notion of Heller
The LDOS: %(E) =∑pαδ(E − Eα)
∆0 = The mean level spacing
∆E = The width of the energy shell
NE = States within the energy shell
N∞ = Participating states
Fqm = Localization measureFig. 38. Ideally ergodic (left) and typically found (right) spectral intensities and en-velopes. Both spectra have the same low resolution envelope.
pα =∣∣∣〈Eα|ψ〉∣∣∣2
tH =2π
∆0, tE =
2π
∆E, NE =
∆E
∆0, N∞ =
[∑α
p2α
]−1
, Fqm ≡N∞NE
The number of states that participate in the dynamics up to time t is:
Nt ≡
trace[ρ(t)2
]−1
=
[2
t
∫ t
0
(1−
τ
t
)P(τ)dτ
]−1
ρ(t) ≡1
t
∫ t
0ρ(t′)dt′
Short times: N qmt ≈ N sc
t ≈ t/tE (based on the classical envelope)
Long times: N clt → N∞ (due to the discreteness of the spectrum)