dynamical quasicondensation of hard-core bosons at finite
TRANSCRIPT
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Lev Vidmar
Penn state University
Dynamical quasicondensation of hard-core bosons at finite momenta
arXiv:1505:05150
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Lev Vidmar
Collaboration (U Munich and MPQ Garching):
S. Langer S.S. Hodgman, M. Schreiber, S. Braun
J.P. Ronzheimer
Dynamical quasicondensation of hard-core bosons at finite momenta
U. SchneiderI. BlochF. Heidrich-Meisner
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Design far from equilibrium systems to
uncover conserved quantities that govern the dynamics (e.g., that give rise to ballistic current)
induce ordered states that do not exist in the equilibrium phase diagram
Goal:
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Bosons on a lattice
Emergence of (quasi) long-range phase coherence when cooling an ideal Bose gas into a Bose-Einstein q = 0 (quasi) condensate
Spontaneous emergence of quasi-long-range order far from equilibrium: quasicondensation at a finite momentum
Here:
Standard picture:
Ɛ(q)
n(q)
vg(q)Ɛ,vg
q(d-1)-π/2 π/2-π π0
Ɛ
ρ(ε)
2J
-2J
(a) (b)
(c)
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Ultracold atoms on optical lattices may realize such novel states, provided that (among others):
Bosons on a lattice
Ɛ(q)
n(q)
vg(q)Ɛ,vg
q(d-1)-π/2 π/2-π π0
Ɛ
ρ(ε)
2J
-2J
(a) (b)
(c)
The initial state can be prepared with high fidelity
The condensation at finite momenta should be resolved from time-of-flight measurement
?
Finite momentum condensationCondensation at q = 0Greiner et al (2002)
(a)
(b)
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Load 39K atoms get BEC
Adiabatically ramp up deep optical lattice
Experiments with ultracold bosons
Dephasing: One boson per site
Ronzheimer et al, PRL (2013)
Initial state preparation
| 0i =Y
i2L0
a†i |;i
Bose-Hubbard modelTime evolution:
H = �JX
hi,ji
a†iaj +U
2
X
i
ni(ni � 1)
U/J ⇡ 20 … very close to the hard-core regime
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H = �JX
hi,ji
a†iaj +U
2
X
i
ni(ni � 1)
Integrability and Bose-Hubbard model
Bose-Hubbard model, U/J = 1 Hard-core bosons
a†iai + aia†i = 1
Hard-core bosons map to noninteracting spinless fermions
Cazalilla et al, Rev. Mod. Phys. (2011)
ni = nfiLocal density:
Integrals of motion: nfk
Mapping to spin-1/2: XX chain
H = �JX
hi,ji
a†iaj = �JX
hi,ji
f†i fj =
X
k
✏knfk
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Initial state and the quench protocol
t = 0: Inhomogeneous initial state
View 1: Bosons in a trap
……
View 2: Domain wall
| 0i =Y
i2L0
a†i |;i
Quantum quench: removal of the confining potential
View 1: Sudden expansion of hard-core bosons on an empty lattice
View 2: Domain wall meltingRigol and Muramatsu (PRL, 2004)
Antal et al (PRE, 1999), Gobert et al (PRE, 2005), Lancaster and Mitra (PRE, 2010), …
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Recent experiments
Experiment
DMRGBallistic dynamics of a strongly interacting 1D system due to integrability
Hard-core bosons in 1D
Fermi-Hubbard model in 2D
Initial state: band insulatorU/J = 0 U/J = 12
Schneider et al, Nature Physics (2012)
Ronzheimer et al, PRL (2013)
Xia et al, Nature Physics (2015)Quantum distillation: upon removal of the confining trap, region of doubly occupied sites in the center get purified
Initial state:
Density distribution
Bose-Hubbard model in 1D and 2D
| 0i =Y
i2L0
a†i |;i
Bose-Hubbard model in 1D
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Theoretical predictions
Dynamical quasicondensation at finite momenta:
Rigol and Muramatsu (PRL, 2004)
(Also: Daley et al, PRA, 2005)
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0 50 100-50-100j
t E (τ
·N)
0.080.120.160.200.24
-π/2 π/2-π π0
t E (τ
·N)
0
1/4
1/2
3/4
1
0
1/4
1/2
3/4
1
0
1
0.8
0.6
0.4
0.2
-1.5 -1 -0.5 0 0.5 1 1.5
10
0.1
|⟨aj a
j+r⟩|
✝
rq (d-1)1
0 1
(a)
(c)
(b)
(d)
nj, n(q) (a.u.)n(
x) (a
.u.)
~
x~
10π
0
(r)
r10 20
tE (τ·N)
^^
0 50 100-50-100j
t E (τ
·N)
0.080.120.160.200.24
-π/2 π/2-π π0
t E (τ
·N)
0
1/4
1/2
3/4
1
0
1/4
1/2
3/4
1
0
1
0.8
0.6
0.4
0.2
-1.5 -1 -0.5 0 0.5 1 1.5
10
0.1
|⟨aj a
j+r⟩|
✝
rq (d-1)1
0 1
(a)
(c)
(b)
(d)
nj, n(q) (a.u.)
n(x)
(a.u
.)~
x~
10π
0
(r)
r10 20
tE (τ·N)
^^
Two time regimes in dynamics
Times tE < (N/4)(~/J)
Bosons: build-up of the quasicondensatesDynamical emergence of long-range correlations
Times Dynamical fermionization
Rigol and Muramatsu (PRL, 2005)
LV et al (PRB, 2013)
tE � N(~/J)
nHCBk (t ! 1) ! nf
k
Asymptotic MDF of HCBs given by integrals of motion
Minguzzi and Gangardt, (PRL, 2005)
Hard-core bosons
Bose-Hubbard model
Tonks-Girardeau gas
Long-lived!
Density distribution
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0 50 100-50-100j
t E (τ
·N)
0.080.120.160.200.24
-π/2 π/2-π π0
t E (τ
·N)
0
1/4
1/2
3/4
1
0
1/4
1/2
3/4
1
0
1
0.8
0.6
0.4
0.2
-1.5 -1 -0.5 0 0.5 1 1.5
10
0.1
|⟨aj a
j+r⟩|
✝
rq (d-1)1
0 1
(a)
(c)
(b)
(d)
nj, n(q) (a.u.)
n(x)
(a.u
.)~
x~
10π
0
(r)
r10 20
tE (τ·N)
^^
0 50 100-50-100j
t E (τ
·N)
0.080.120.160.200.24
-π/2 π/2-π π0
t E (τ
·N)
0
1/4
1/2
3/4
1
0
1/4
1/2
3/4
1
0
1
0.8
0.6
0.4
0.2
-1.5 -1 -0.5 0 0.5 1 1.5
10
0.1
|⟨aj a
j+r⟩|
✝
rq (d-1)1
0 1
(a)
(c)
(b)
(d)
nj, n(q) (a.u.)
n(x)
(a.u
.)~
x~
10π
0
(r)
r10 20
tE (τ·N)
^^
Dynamical emergence of long-range correlations
……
0 50 100-50-100j
t E (τ
·N)
0.080.120.160.200.24
-π/2 π/2-π π0
t E (τ
·N)
0
1/4
1/2
3/4
1
0
1/4
1/2
3/4
1
0
1
0.8
0.6
0.4
0.2
-1.5 -1 -0.5 0 0.5 1 1.5
10
0.1
|⟨aj a
j+r⟩|
✝
rq (d-1)1
0 1
(a)
(c)
(b)
(d)
nj, n(q) (a.u.)
n(x)
(a.u
.)~
x~
10π
0
(r)
r10 20
tE (τ·N)
^^
x = (j � j0)/(2tE)
Each half of the chain: Current carrying state
Emergence of power-law correlations
A(r) ⇠ r�1/2
�(r) = ±⇡
2r
ha†jaj+ri = A(r)ei�(r)
0 50 100-50-100j
t E (τ
·N)
0.080.120.160.200.24
-π/2 π/2-π π0
t E (τ
·N)
0
1/4
1/2
3/4
1
0
1/4
1/2
3/4
1
0
1
0.8
0.6
0.4
0.2
-1.5 -1 -0.5 0 0.5 1 1.5
10
0.1
|⟨aj a
j+r⟩|
✝
rq (d-1)1
0 1
(a)
(c)
(b)
(d)
nj, n(q) (a.u.)
n(x)
(a.u
.)~
x~
10π
0
(r)
r10 20
tE (τ·N)
^^
… ground-state exponent
Lancaster and Mitra (PRE, 2010)
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Each half of the chain: Current carrying state
Dynamical emergence of long-range correlations
Emergence of power-law correlations
A(r) ⇠ r�1/2
�(r) = ±⇡
2r
ha†jaj+ri = A(r)ei�(r)
0 50 100-50-100j
t E (τ
·N)
0.080.120.160.200.24
-π/2 π/2-π π0
t E (τ
·N)
0
1/4
1/2
3/4
1
0
1/4
1/2
3/4
1
0
1
0.8
0.6
0.4
0.2
-1.5 -1 -0.5 0 0.5 1 1.5
10
0.1
|⟨aj a
j+r⟩|
✝
rq (d-1)1
0 1
(a)
(c)
(b)
(d)
nj, n(q) (a.u.)
n(x)
(a.u
.)~
x~
10π
0
(r)
r10 20
tE (τ·N)
^^
… ground-state exponent
Lancaster and Mitra (PRE, 2010)
0 50 100-50-100j
t E (τ
·N)
0.080.120.160.200.24
-π/2 π/2-π π0
t E (τ
·N)
0
1/4
1/2
3/4
1
0
1/4
1/2
3/4
1
0
1
0.8
0.6
0.4
0.2
-1.5 -1 -0.5 0 0.5 1 1.5
10
0.1
|⟨aj a
j+r⟩|
✝
rq (d-1)1
0 1
(a)
(c)
(b)
(d)
nj, n(q) (a.u.)
n(x)
(a.u
.)~
x~
10π
0
(r)
r10 20
tE (τ·N)
^^
Singularities in the quasimomentum distribution at finite quasimomenta
n(q) =1
L
X
j,l
e�iq(j�l)dha†jali
n(q)
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Dynamical emergence of long-range correlations
Power-law correlations emerge spontaneously
0 50 100-50-100j
t E (τ
·N)
0.080.120.160.200.24
-π/2 π/2-π π0
t E (τ
·N)
0
1/4
1/2
3/4
1
0
1/4
1/2
3/4
1
0
1
0.8
0.6
0.4
0.2
-1.5 -1 -0.5 0 0.5 1 1.5
10
0.1
|⟨aj a
j+r⟩|
✝
rq (d-1)1
0 1
(a)
(c)
(b)
(d)
nj, n(q) (a.u.)
n(x)
(a.u
.)~
x~
10π
0
(r)
r10 20
tE (τ·N)
^^
To remember:
Singularities in the quasimomentum distribution at finite quasimomenta
n(q) =1
L
X
j,l
e�iq(j�l)dha†jali
n(q)
(there is no coherence in the initial state!)
There are two independent sources of coherence
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Experimental realization
Dynamical quasicondensation at finite momenta:
arXiv:1505:05150
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norm
aliz
ed d
ensi
ty (a
.u.)
tE = 0τ tE = 7τ tE = 36τ
expa
nsio
ntim
e-of
-flig
ht
tE
tTOF
tE = 14τ(a)
time-of-flight position (µm)-200 0 200 -200 0 200 -200 0 200 -200 0 200
(f) (g) (h) (i)
-100 0 100 -100 0 100 -100 0 100 -100 0 100in situ position (d)
(b) (c) (d) (e) experimenttheory
t = 0
t = tE
t = tE+tTOF norm
aliz
ed d
ensi
ty (a
.u.)
Expansion in a lattice (with interactions!)
Expansion in a free space (without interactions)
Time-of-flight (TOF) measurement
In-situ absorption imaging
| (t)i = e�iHt| 0i
Measure density distribution
Measure momentum distribution
nj
nk
Experimental sequence
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norm
aliz
ed d
ensi
ty (a
.u.)
tE = 0τ tE = 7τ tE = 36τ
expa
nsio
ntim
e-of
-flig
ht
tE
tTOF
tE = 14τ(a)
time-of-flight position (µm)-200 0 200 -200 0 200 -200 0 200 -200 0 200
(f) (g) (h) (i)
-100 0 100 -100 0 100 -100 0 100 -100 0 100in situ position (d)
(b) (c) (d) (e) experimenttheory
t = 0
t = tE
t = tE+tTOF norm
aliz
ed d
ensi
ty (a
.u.)
Results: density distribution in the lattice
Theoretical modeling: two input parameters only | 0i =Y
i2L0
a†i |;i
Total number of particles in the 3D cloud of isolated 1D chains
Finite entropy in the system, which results in holes in the initial state
Si = �kB(ni log ni + (1� ni) log(1� ni))
S/N3D =X
i=(x,y,z)
Si
/N3D ⇡ 1.2kB
probability to find a particle at site i
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norm
aliz
ed d
ensi
ty (a
.u.)
tE = 0τ tE = 7τ tE = 36τ
expa
nsio
ntim
e-of
-flig
ht
tE
tTOF
tE = 14τ(a)
time-of-flight position (µm)-200 0 200 -200 0 200 -200 0 200 -200 0 200
(f) (g) (h) (i)
-100 0 100 -100 0 100 -100 0 100 -100 0 100in situ position (d)
(b) (c) (d) (e) experimenttheory
t = 0
t = tE
t = tE+tTOF norm
aliz
ed d
ensi
ty (a
.u.)
Results: density distribution in the lattice
0 10 20 30 40 50tE (τ)
50
100
Rc (
d)
Density dynamics consistent with ballistic expansionRonzheimer et al, PRL (2013)
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norm
aliz
ed d
ensi
ty (a
.u.)
tE = 0τ tE = 7τ tE = 36τ
expa
nsio
ntim
e-of
-flig
ht
tE
tTOF
tE = 14τ(a)
time-of-flight position (µm)-200 0 200 -200 0 200 -200 0 200 -200 0 200
(f) (g) (h) (i)
-100 0 100 -100 0 100 -100 0 100 -100 0 100in situ position (d)
(b) (c) (d) (e) experimenttheory
t = 0
t = tE
t = tE+tTOF norm
aliz
ed d
ensi
ty (a
.u.)
Results: TOF distribution
norm
aliz
ed d
ensi
ty (a
.u.)
tE = 0τ tE = 7τ tE = 36τ
expa
nsio
ntim
e-of
-flig
ht
tE
tTOF
tE = 14τ(a)
time-of-flight position (µm)-200 0 200 -200 0 200 -200 0 200 -200 0 200
(f) (g) (h) (i)
-100 0 100 -100 0 100 -100 0 100 -100 0 100in situ position (d)
(b) (c) (d) (e) experimenttheory
t = 0
t = tE
t = tE+tTOF norm
aliz
ed d
ensi
ty (a
.u.)
norm
aliz
ed d
ensi
ty (a
.u.)
tE = 0τ tE = 7τ tE = 36τ
expa
nsio
ntim
e-of
-flig
ht
tE
tTOF
tE = 14τ(a)
time-of-flight position (µm)-200 0 200 -200 0 200 -200 0 200 -200 0 200
(f) (g) (h) (i)
-100 0 100 -100 0 100 -100 0 100 -100 0 100in situ position (d)
(b) (c) (d) (e) experimenttheory
t = 0
t = tE
t = tE+tTOF norm
aliz
ed d
ensi
ty (a
.u.)
Comparison: theory - experiment
Very good agreement for both the number of peaks as well as the position of peaks:
Main peaks: very close to
The number of side peaks consistent with emergence of two independent quasicondensates
~q = ±(⇡/2)(~/d)
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tTOF = 6ms tTOF = 10ms tTOF = 12ms tTOF = 15ms
02468
101214
corrected time-of-flight position (µm)
corrected time-of-flight position (µm)t T
OF (m
s)lin
e de
nsity
(a.u
.)
(a) (b) (c) (d)
0-600 600 0-600 600 0-600 600 0-600 600
-600 -400 -200 0 200 400 600
(e)
Fit the experimental TOF distribution with six gaussians
Very similar results: the two main peaks very close to
norm
aliz
ed d
ensi
ty (a
.u.)
tE = 0τ tE = 7τ tE = 36τ
expa
nsio
ntim
e-of
-flig
ht
tE
tTOF
tE = 14τ(a)
time-of-flight position (µm)-200 0 200 -200 0 200 -200 0 200 -200 0 200
(f) (g) (h) (i)
-100 0 100 -100 0 100 -100 0 100 -100 0 100in situ position (d)
(b) (c) (d) (e) experimenttheory
t = 0
t = tE
t = tE+tTOF norm
aliz
ed d
ensi
ty (a
.u.)
Results: TOF distribution (fitting)
~q = ±(⇡/2)(~/d)
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More about theoretical modeling
Typical initial states zero entropy
finite entropy
TOF distribution nTOF(r) =X
rj ,rl
w⇤0(r � rj , tTOF)w0(r � rl, tTOF)ha†rj arli
nTOF(x) =1
d
r↵
⇡
e
�x
2↵
X
j,l
e
x(l+j)↵e
� 12 (l
2+j
2)↵e
�ix(l�j)�e
i(l2�j
2) �2 ha†
j
a
l
iGerbier et al, PRL (2008)
One-particle density matrix
tE = 10⌧ tE = 14⌧
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norm
aliz
ed d
ensi
ty (a
.u.)
tE = 0τ tE = 7τ tE = 36τ
expa
nsio
ntim
e-of
-flig
ht
tE
tTOF
tE = 14τ(a)
time-of-flight position (µm)-200 0 200 -200 0 200 -200 0 200 -200 0 200
(f) (g) (h) (i)
-100 0 100 -100 0 100 -100 0 100 -100 0 100in situ position (d)
(b) (c) (d) (e) experimenttheory
t = 0
t = tE
t = tE+tTOF norm
aliz
ed d
ensi
ty (a
.u.)
Instead of the generic thermalization dynamics, the atoms bunch at one distinct momentum
The quasi-long-range order emerges spontaneously far from equilibrium, where it is very surprising to find coherence at all
The role of integrability and dimensionality?
Emergence of long-range order in steady states of generic systems?
Conclusions
Open questions
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Thank you
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0 20 40 60 80 100N
0
0.1
0.2
0.3
0.4P
(N
)
S = 0S > 0
Distribution of probabilities P(N) to find particles in chains with particle number N
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One-particle density matrix
tE = 10⌧ tE = 14⌧
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Dimensionality
Hard-core bosons on two-leg ladder: fermionic momenta not conserved
J?/J = 0 J?/J = 0.5 J?/J = 1
Density profiles
t=0 t>0
LV, Langer, McCulloch, Schneider, Schollwöck, Heidrich-Meisner, PRB (2013)
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BHM at finite interactions
U=4 U=10
Expansion from Mott insulator
Expansion from superfluid
U/J(U/J)c ⇡ 3.4
hard-core U=0
Density profiles are identical for all bosonic and fermionic Mott insulators
Virtually identical to the ones of non-interacting fermions
Initial state at finite U/J
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1D Mott insulators (bosons and fermions)
Asymptotic expansion dynamics governed by non-interacting fermions
Dynamical fermionization for Bose-Hubbard model
Particle-hole symmetric MDF
Virtually identical density profiles
at asymptotic times …
Flat velocity distribution n(vk)