Review of Holographic (and other) computations of...
Transcript of Review of Holographic (and other) computations of...
Holographic(and other)
computations of
Review of
computations of Entanglement Entropy, and its role in gravity
Entanglement Entropy
• in QFT, typically introduce a (smooth) boundary or entanglingsurface which divides the space into two separate regions
• integrate out degrees of freedom in “outside” region• remaining dof are described by a density matrix
• what is entanglement entropy?general tool; divide quantum system into two parts and useentropy as measure of correlations between subsystems
AB
calculate von Neumann entropy:
Entanglement Entropy
AB
• remaining dof are described by a density matrix
calculate von Neumann entropy:
R
• result is UV divergent! dominated by short-distance correlations
= spacetime dimension
= short-distance cut-off• must regulate calculation:
• careful analysis reveals geometric structure, eg,
Entanglement Entropy
AB
• remaining dof are described by a density matrix
calculate von Neumann entropy:
R
= spacetime dimension
= short-distance cut-off• must regulate calculation:
• leading coefficients sensitive to details of regulator, eg, • find universal information characterizing underlying QFT insubleading terms, eg,
General comments on Entanglement Entropy:
• nonlocal quantity which is (at best) very difficult to measure
• in condensed matter theory: diagnostic to characterize quantumcritical points, quantum spin fluids or topological phases
• in quantum information theory: useful measure of quantum
no accepted experimental procedure
• in quantum information theory: useful measure of quantumentanglement (a computational resource)
Where did “Entanglement Entropy” come from? black holes
• recall that leading term obeys “area law”:
suggestive of Bekenstein-Hawking formula if
(Sorkin `84; Bombelli, Koul, Lee & Sorkin; Srednicki; Frolov & Novikov; . . .)
• Sorkin ’84: looking for origin of black hole entropy
General comments on Entanglement Entropy:
(Sorkin `84; Bombelli, Koul, Lee & Sorkin; Srednicki; Frolov & Novikov; . . .)
• problem?: leading singularity not universal; regulator dependent
• active topic in 90’s but story left unresolved (return to this later)
• recently considered in AdS/CFT correspondence(Ryu & Takayanagi `06)
AdS/CFT Correspondence:
Bulk: gravity with negative Λin d+1 dimensions
anti-de Sitterspace
Boundary: quantum field theoryin d dimensions
conformalfield theory
“holography”
energyradius
Holographic Entanglement Entropy:(Ryu & Takayanagi `06)
AB
AdS boundary
AdS bulk
boundaryconformal field
theory
gravitationalpotential/redshiftAdS bulk
spacetime
potential/redshift
• “UV divergence” because area integral extends to
Holographic Entanglement Entropy:
AB
AdS boundary
(Ryu & Takayanagi `06)
cut-off in boundary CFT:
cut-off surface
• finite result by stopping radial integral at large radius:
short-distance cut-off in boundary theory:
• “UV divergence” because area integral extends to
Holographic Entanglement Entropy:
AB
AdS boundary
(Ryu & Takayanagi `06)
cut-off in boundary CFT:
central charge(counts dof) “Area Law”
cut-off surface
Holographic Entanglement Entropy:
AB
AdS boundary
(Ryu & Takayanagi `06)
cut-off in boundary CFT:
cut-off surface
general expression (as desired):
(d even)
(d odd)universal contributions
Holographic Entanglement Entropy:
conjecture
Extensive consistency tests:
(Ryu & Takayanagi `06)
1) leading contribution yields “area law”
2) recover known results of Calabrese & Cardyfor d=2 CFT
(also result for thermal ensemble)
Holographic Entanglement Entropy:
conjecture
Extensive consistency tests:
(Ryu & Takayanagi `06)
3) in a pure state
and both yield same bulk surface V
AdSboundary
and both yield same bulk surface V
Holographic Entanglement Entropy:
conjecture
Extensive consistency tests:
(Ryu & Takayanagi `06)
3) in a pure state
and both yield same bulk surface V
AdSboundary
and both yield same bulk surface V
cf: thermal ensemble ≠ pure state horizon in bulk
AdS/CFT Dictionary: black holethermal bath
Holographic Entanglement Entropy:
conjecture
Extensive consistency tests:
(Ryu & Takayanagi `06)
4) Entropy of eternal black hole =entanglement entropy of boundary CFT & thermofield double
(Headrick)(Headrick)
boundaryCFT
thermofielddouble
extremal surface =bifurcation surface
Holographic Entanglement Entropy:
conjecture
Extensive consistency tests:
(Ryu & Takayanagi `06)
5) sub-additivity:(Headrick & Takayanagi)
[ “all” other inequalities: Hayden, Headrick & Maloney]
Holographic Entanglement Entropy:
conjecture
Extensive consistency tests:
(Ryu & Takayanagi `06)
4) Entropy of eternal black hole =entanglement entropy of boundary CFT & thermofield double
5) sub-additivity:(Headrick & Takayanagi)
for more general holographic framework, expect
includes correctionscorrections
(Hayden, Headrick & Maloney)
some progress with classical higher curvature gravity:
for more general holographic framework, expect
• note is not unique! and is wrong choice!
• correct choice understood for “Lovelock theories”
(Hung, Myers & Smolkin)(deBoer, Kulaxizi & Parnachev)
(Solodukhin)• test with universal term for d=4 CFT: (Solodukhin)
thermal entropy
universal contribution
c a
• test with universal term for d=4 CFT:
Topics currently trending in Holographic SEE:
• suggest C/F-theorems
• diagnostic of holo-fermi surfaces
• probe of holo-quantum quenches
• probe of holo-RG flows
(Myers & Sinha; Liu & Mezei; . . .)
(Ogawa, Takayanagi & Ugajin; Huijse, Sachdev & Swingle; . . . )
(Albash & Johnson; Myers & Singh; . . .)
(Abajo-Arrastia, Aparicio, Lopez; Balasubramanian et al; . . .)
• probe of holo-RG flows
• probe of holo-insulator/superconductor transition
• probe of holo-QFT in curved/deSitter space
• probe of holo-logarithmic CFT’s
• probe of holo-fractionalized states
(Albash & Johnson; Myers & Singh; . . .)
● ● ● ●
(Grumiller, Rieldler, Rosseel & Zojer)
(Maldacena & Pimental)
(Albash, Johnson & Macdonald; Hartnoll & Huijse, . . .)
(Albash & Johnson; Cai, He, Li & Li . . .)
????
Lessons for bulk gravity theory:
AdS/CFT Dictionary:
Bulk: black holeBoundary: thermal plasma
Temperature Temperature
Energy Energy
Entropy Entropy
Lessons for bulk gravity theory:
(entanglement entropy)boundary
= (entropy associated with extremal surface)bulk
What Entropy?/Entropy of what?
extremalsurface
What are the rules?
(eg, Hubney, Rangamani & Takayanagi)
not black hole! not horizon!not causal domain!
Proposal : Geometric Entropy• in a theory of quantum gravity, for any sufficiently large regionwith a smooth boundary in a smooth background (eg, flat space),leading contribution to entanglement entropy takes the form:
(Bianchi & Myers)
AB
• in QG, (short range) quantum entanglement corresponding to area law is a signature of macroscopic spacetime geometry
(entanglement entropy)boundary
= (entropy associated with extremal surface)bulk
not black hole! not horizon!not causal domain!
• R&T construction assigns entropy to bulkregions with “unconventional” boundaries:
Lessons for bulk gravity theory:
not causal domain!
extremalsurface
• indicates S BH applies more broadly!
• what about extremization?
needed to make match above
• other surfaces might be expected to giveother entropic measures of entanglementin boundary theory(Hubeny & Rangamani; Balasubramanian, McDermott & van Raamsdonk)
Proposal : Geometric Entropy• in a theory of quantum gravity, for any sufficiently large regionwith a smooth boundary in a smooth background (eg, flat space),there is an entanglement entropy which takes the form:
• evidence comes from several directions:
(Bianchi & Myers)
• evidence comes from several directions:
1. holographic in AdS/CFT correspondence
2. QFT renormalization of
3. Randall-Sundrum 2 model
4. spin-foam approach to quantum gravity
5. Jacobson’s “thermal origin” of gravity
Where did “Entanglement Entropy” come from? black holes
• recall that leading term obeys “area law”:
suggestive of BH formula if (Sorkin `84; Bombelli, Koul, Lee & Sorkin; Srednicki; Frolov & Novikov)
• Sorkin ’84: looking for origin of black hole entropy
• problem?: leading singularity not universal; regulator dependent• problem?: leading singularity not universal; regulator dependent
• resolution: this singularity represents contribution of “low energy”d.o.f. which actually renormalizes “bare” area term
(Susskind & Uglum)
both coefficients are regulator dependentbut for a given regulator should match!
BH Entropy ~ Entanglement Entropy (Susskind & Uglum)
both coefficients are regulator dependentbut for a given regulator should match!
• seems matching is not always working??
• “a beautiful killed by ugly facts”??
• seems matching is not always working??(Demers, Lafrance & Myers; Kabat, Strassler, Frolov, Solodukhin, Fursaev, . . . )
• all numerical factors seem to be resolved! (Cooperman & Luty)
matching of area term works for any QFT (s=0,1/2, 1, 3/2)to all orders in perturbation theory for any Killing horizon
• technical difficulties for spin-2 graviton
• results apply for Rindler horizon in flat space♥(some technical/conceptual issues may remain! Jacobson & Satz)
BH Entropy ~ Entanglement Entropy (Susskind & Uglum)
both coefficients are regulator dependentbut for a given regulator should match!
• “a beautiful killed by ugly facts”??
• result “unsatisfying”: • result “unsatisfying”:
where did bare term come from?
• formally “off-shell” method is precisely calculation of SEE
(Susskind & Uglum; Callan & Wilczek; Myers & Sinha: extends to Swald)
• challenge: understand microscopic d.o.f. of quantum gravityAdS/CFT: eternal black hole (or any Killing horizon)
(Maldacena; van Raamsdonk et al; Casini, Huerta & Myers)
AB
• first step in calculation of SEE is to determine
• return to considerations of SEE of general region in some QFT
• encodes standard correlators, eg, if global vacuum:
• by causality, describes physics throughout causal domain
AB
Entanglement Hamiltonian:
• hermitian and positive semi-definite, hence
= modular or entanglement Hamiltonian
• formally can consider evolution by
• unfortunately is nonlocal and flow is nonlocal/not geometric
AB
Entanglement Hamiltonian:
• hermitian and positive semi-definite, hence
• explicitly known in only a few instances
• most famous example: Rindler wedge
ABboost generator●
= modular or entanglement Hamiltonian
A
Entanglement Hamiltonian:Can this formalism provide
insight for “area law” term in S EE?
• zoom in on infinitesimal patch of
region looks like flat spacelooks like Rindler horizon
• assume Hadamard-like statecorrelators have standard UV sing’s
• UV part of same as in flat space• must have Rindler term:
• must have Rindler term:
A
Entanglement Hamiltonian:Can this formalism provide
insight for “area law” term in S EE?
• UV part of must besame as in flat space
for each infinitesimal patch:
• must have Rindler term:
hence SEE must contain divergent area law contribution!
• invoke Cooperman & Luty: area law divergence matchesprecisely renormalization of :
for any large region of smooth geometry!!
Rindler yields area law; hence
A
Entanglement Hamiltonian:Can this formalism provide
insight for “area law” term in S EE?
• challenge: understand microscopic d.o.f. of quantum gravity
• we can formulate a formal geometric argument analogous tothe “off-shell” method for black holes (or Rindler horizons)
• Cooperman & Luty: area law divergencematches precisely renormalization of :
for any large region of smooth geometry!!
Proposal : Geometric Entropy• in a theory of quantum gravity, for any sufficiently large regionwith a smooth boundary in a smooth background (eg, flat space),there is an entanglement entropy which takes the form:
• evidence comes from several directions:
(Bianchi & Myers)
• evidence comes from several directions:
1. holographic in AdS/CFT correspondence
2. QFT renormalization of
3. Randall-Sundrum 2 model
4. spin-foam approach to quantum gravity
5. Jacobson’s “thermal origin” of gravity
MERA & Holography:
• Multi-scale Entanglement Renormalization Ansatz: approximateand efficient approach to build ground-state wavefunction ofcritical lattice models (Vidal; . . . )
• close connection between MERA and AdS/CFT (Swingle)
disentanglers :remove short-range
entanglement
isometries :decimate lattice
MERA & Holography:
• Multi-scale Entanglement Renormalization Ansatz: approximateand efficient approach to build ground-state wavefunction ofcritical lattice models (Vidal; . . . )
• close connection between MERA and AdS/CFT (Swingle)
• short-hand:
• question: where is the entanglement entropy?
UV
IR● ● ● ●
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• introduce conjugate circuit• trace over exterior bonds
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• introduce conjugate circuit• trace over exterior bonds
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• SEE and SRen are unchanged by• 2k (=Leff) bonds → 1 bond in k layers• each layer contributes c/3 to SEE
SEE = c/3 log(Leff)
● ● ● ●
• SEE and SRen are unchanged by
B
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• SEE and SRen are unchanged by
B
● ● ● ●
• only narrow band of circuitcontributes to SEE and SRen
B
● ● ● ●
• only narrow band of circuitcontributes to SEE and SRen
MERA & Holography:
• Multi-scale Entanglement Renormalization Ansatz: approximateand efficient approach to build ground-state wavefunction ofcritical lattice models (Vidal; . . . )
• close connection between MERA and AdS/CFT (Swingle)
• question: where is the entanglement entropy?
only narrow band of circuit contributes to SEE and SRen
• common theme: long-range entanglement short-range entanglement
only narrow band of circuit contributes to SEE and SRen
• RT prescription: SEE depends on geometry near extremal surface
• MERA might provide insight for questions:
nature of extremization procedure?information in non-extremal surfaces? calculating Renyi entropies?
Conclusions:
• holographic entanglement entropy is part of an interestingdialogue has opened between string theorists and physicistsin a variety of fields (eg, condensed matter, nuclear physics, . . .)
• potential to learn lessons about issues in boundary theory
Dialogue:
Lots to explore!
• potential to learn lessons about issues in boundary theory
• potential to learn lessons about issues in quantum gravity in bulk