Entanglement Entropy with Current & Chemical Potential Bom Soo Kim Department of Physics and Astronomy, University of Kentucky, Lexington 40506

Great Lakes Strings conference University of Cincinnati May 5-7, 2017 Based on 1705.01859

Partition Function & EE with J & µ (3 slides) - Twisted boundary condition & background gauge fields - Partition Function with J & µ - General formula for EE & R´enyi entropy with J & µ

Applications (6 slides)

˜µ Twisted B.C. & A • Dirac fermion in the presence of background gauge fields : S=

1 2π

Z

¯ µ (∂µ + iAµ ) ψ , d 2 x i ψγ

– on torus with τ = τ1 + iτ2 1 – for coordinates ζ = 2π (s + it) is identified as ζ ≡ ζ + 1 ≡ ζ + τ .

• twisted boundary conditions ψ(t, s) = e −2πia ψ(t, s + 2π) = e −2πib ψ(t + 2πτ2 , s + 2πτ1 ) . ˜ µ = (˜ ˜ ≡ periodic Dirac fermion with flat gauge connection A µ, J) n a=J ˜ = πi [(b−τ a)d ζ¯−(b − τ¯a)dζ] = ads + b−aτ1 dt → A . τ2 τ2 b = τ1 J˜ +iτ2 µ ˜ Di Francesco, Mathieu & Senechal, “Conformal Field Theory,” 1997; Hori, et. al. “Mirror symmetry,” 2003

˜µ Twisted B.C. & A • Dirac fermion in the presence of background gauge fields : S=

1 2π

Z

¯ µ (∂µ + iAµ ) ψ , d 2 x i ψγ

– on torus with τ = τ1 + iτ2 1 – for coordinates ζ = 2π (s + it) is identified as ζ ≡ ζ + 1 ≡ ζ + τ .

• twisted boundary conditions ψ(t, s) = e −2πia ψ(t, s + 2π) = e −2πib ψ(t + 2πτ2 , s + 2πτ1 ) . ˜ µ = (˜ ˜ ≡ periodic Dirac fermion with flat gauge connection A µ, J) ˜ = πi [(b−τ a)d ζ¯−(b − τ¯a)dζ] = ads + b−aτ1 dt A τ2 τ2



n

a = J˜ . b = τ1 J˜ +iτ2 µ ˜

Di Francesco, Mathieu & Senechal, “Conformal Field Theory,” 1997; Hori, et. al. “Mirror symmetry,” 2003

Partition function 2   −2  1/2−a  2H Z[a,b] = |{z} Tr e −2πi(b−1/2)FA e −2πiτ1 P e| −2πτ ϑ b−1/2 (0, τ ) , {z } = |η(τ )|

trace over H (twisted B.C. a for s ∼ s + 2π)

euclidean time evolution t → t +2πτ2 with H – s → s −2πτ1 with e −2πiτ1 P , P momentum – phase rotation e −2πi(b−1/2)FA , fermion # FA ,

Q∞ n 2πiτ n=1 (1 − q ) with q = e h i P (n+α)2 /2 2πi(z+β)(n+α) Jacobi theta function ϑ α (z|τ ) = q e n∈Z β h i h i NS(R)-NS sector: ϑ3 (z|τ ) = ϑ 00 (z|τ ), ϑ2 (z|τ ) = ϑ 1/2 (z|τ ) 0

– Dedekind function η(τ ) = q 1/24 – –

Di Francesco, Mathieu & Senechal, “Conformal Field Theory,” 1997; Hori, et. al. “Mirror symmetry,” 2003

• including current J and chemical potential µ: 2     (τ1 J +iτ2 µ|τ ) . Tr e 2πi(τ1 J+iτ2 µ+b−1/2)FA e −2πiτ1 P e −2πτ2 H = |η(τ )|−2 ϑ 1/2−a−J b−1/2

Partition function 2   −2  1/2−a  2H Z[a,b] = |{z} Tr e −2πi(b−1/2)FA e −2πiτ1 P e| −2πτ ϑ b−1/2 (0, τ ) , {z } = |η(τ )|

trace over H (twisted B.C. a for s ∼ s + 2π)

euclidean time evolution t → t +2πτ2 with H – s → s −2πτ1 with e −2πiτ1 P , P momentum – phase rotation e −2πi(b−1/2)FA , fermion # FA ,

Q∞ n 2πiτ n=1 (1 − q ) with q = e h i P (n+α)2 /2 2πi(z+β)(n+α) Jacobi theta function ϑ α (z|τ ) = q e n∈Z β h i h i NS(R)-NS sector: ϑ3 (z|τ ) = ϑ 00 (z|τ ), ϑ2 (z|τ ) = ϑ 1/2 (z|τ ) 0

– Dedekind function η(τ ) = q 1/24 – –

Di Francesco, Mathieu & Senechal, “Conformal Field Theory,” 1997; Hori, et. al. “Mirror symmetry,” 2003

• including current J and chemical potential µ: 2     (τ1 J +iτ2 µ|τ ) . Tr e 2πi(τ1 J+iτ2 µ+b−1/2)FA e −2πiτ1 P e −2πτ2 H = |η(τ )|−2 ϑ 1/2−a−J b−1/2

Partition function 2   −2  1/2−a  2H Z[a,b] = |{z} Tr e −2πi(b−1/2)FA e −2πiτ1 P e| −2πτ ϑ b−1/2 (0, τ ) , {z } = |η(τ )|

trace over H (twisted B.C. a for s ∼ s + 2π)

euclidean time evolution t → t +2πτ2 with H – s → s −2πτ1 with e −2πiτ1 P , P momentum – phase rotation e −2πi(b−1/2)FA , fermion # FA ,

Q∞ n 2πiτ n=1 (1 − q ) with q = e h i P (n+α)2 /2 2πi(z+β)(n+α) α Jacobi theta function ϑ β (z|τ ) = e n∈Z q h i h i NS(R)-NS sector: ϑ3 (z|τ ) = ϑ 00 (z|τ ), ϑ2 (z|τ ) = ϑ 1/2 (z|τ ) 0

– Dedekind function η(τ ) = q 1/24 – –

Di Francesco, Mathieu & Senechal, “Conformal Field Theory,” 1997; Hori, et. al. “Mirror symmetry,” 2003

• including current J and chemical potential µ: 2     1/2−a−J Tr e 2πi(τ1 J+iτ2 µ+b−1/2)FA e −2πiτ1 P e −2πτ2 H = |η(τ )|−2 ϑ b−1/2+τ (0|τ ) 1 J+iτ2 µ 2   (τ1 J +iτ2 µ|τ ) . = |η(τ )|−2 ϑ 1/2−a−J b−1/2

EE & R´ enyi entropy Calabrese and Cardy 2004, 2009; Casini, Fosco and Huerta 2005; Nishioka, Ryu and Takayanagi 2009

– For a subsystem A with `t in total system 2πL – replica of n-copies in Path integral: Zn orbifold theory on torus – signs of Tr and connections of copies: σ±k operators with ∆k = k 2 /2n2 Sn =

1 1 h [log Tr(ρA )n ] = log 1−n 1−n

hσk (`t )σ−k (0)i =

n−1/2

Y

i hσk (`t )σ−k (0)i = Sn0 + Snµ,J ,

k=−(n−1)/2

2k 2 /n2 ϑ[1/2−a−J ]( k `t + τ1 J + iτ2 µ|τ ) 2 b−1/2 n 2πL × . 1/2−a−J `t ϑ[1/2 ]( ϑ[ ](τ J + iτ µ|τ ) |τ ) 1 2 1/2 2πL b−1/2 2πη(τ )3

– n → 1 to obtain EE – factorize into two parts: one independent of (J, µ): well studied – EE(µ) previously studied in Ogawa, Takayanagi and Ugajin 2011; Herzog and Nishioka 2013 – we study the R´ eny entropy and EE depending both on (J, µ)! – straightforward to generalize for multiple intervals. Herzog and Nishioka 2013 – NS-NS sector: a + J = 1/2, b = 1/2; R-NS sector: a + J = 0, b = 1/2.

EE & R´ enyi entropy Calabrese and Cardy 2004, 2009; Casini, Fosco and Huerta 2005; Nishioka, Ryu and Takayanagi 2009

– For a subsystem A with `t in total system 2πL – replica of n-copies in Path integral: Zn orbifold theory on torus – signs of Tr and connections of copies: σ±k operators with ∆k = k 2 /2n2 Sn =

1 1 h [log Tr(ρA )n ] = log 1−n 1−n

hσk (`t )σ−k (0)i =

n−1/2

Y

i hσk (`t )σ−k (0)i = Sn0 + Snµ,J ,

k=−(n−1)/2

2k 2 /n2 ϑ[1/2−a−J ]( k `t + τ1 J + iτ2 µ|τ ) 2 b−1/2 n 2πL × . 1/2−a−J `t ϑ[1/2 ]( ϑ[ ](τ J + iτ µ|τ ) |τ ) 1 2 1/2 2πL b−1/2 2πη(τ )3

– n → 1 to obtain EE – factorize into two parts: one independent of (J, µ): well studied – EE(µ) previously studied in Ogawa, Takayanagi and Ugajin 2011; Herzog and Nishioka 2013 – we study the R´ eny entropy and EE depending both on (J, µ)! – straightforward to generalize for multiple intervals. Herzog and Nishioka 2013 – NS-NS sector: a+J = 1/2, b = 1/2; R-NS sector: a+J = 0, b = 1/2.

Partition Function & EE with J & µ (3 slides)

Applications – Entropies & Chemical potential in T → 0 – Entropies & Current in T → 0

(2 slides)

– Entropies & large radius limit

(1 slides)

– Mutual information with J & µ

(1 slide)

(2 slides)

EE (µ) for NS-NS sector – NS-NS (a = b = 1/2) for J = τ1 = 0: Snµ =

1 h 1−n

iβµ ϑ[1/2−a−J b−1/2 ](τ1 J + iτ2 µ|τ ) → ϑ3 ( 2π |iβ)

n−1/2

`t ϑ3 ( kn 2πL + iβµ |iβ) 2 i 2π , log iβµ ϑ3 ( 2π |iβ) k=−(n−1)/2

X

m m−1/2 )(1+y −1 q m−1/2 ), m=1 (1−q )(1+yq ` −βµ+i k t − βµ − β n L , y2 = e y1 = e , q =e

– ϑ3 (z|τ ) =

Q∞

– – taking β = 2πτ2 → ∞ limit

Snµ =

=

1 h 1−n

n−1/2

∞ Y (1−q m )(1+y1 q m−1/2 )(1+y1−1 q m−1/2 ) 2 i log m−1/2 )(1+y −1 q m−1/2 ) m 2 m=1 (1−q )(1+y2 q k=−(n−1)2

X

∞ i 2 h X (−1)l−1 e −lβµ +e lβµ  l`t  l`t  sin csc −n , lβ(m−1/2) 1−n l,m=1 l 2L 2Ln e

µ Sn=1 =2

∞ X l`t i (−1)l−1 cosh (lβµ) h l`t 1− cot . l sinh (lβ/2) 2L 2L l=1

– valid for y2 q 1/2 , y2−1 q 1/2 < 1 ⇒ −1/2 < µ < 1/2 & S → 0 for β → ∞. – same for other constant µ due to the periodicity S(µ) = S(µ + 1) = S(µ − 1).

EE (µ) for NS-NS sector – NS-NS (a = b = 1/2) for J = τ1 = 0: Snµ =

1 h 1−n

iβµ ϑ[1/2−a−J b−1/2 ](τ1 J + iτ2 µ|τ ) → ϑ3 ( 2π |iβ)

n−1/2

`t ϑ3 ( kn 2πL + iβµ |iβ) 2 i 2π , log iβµ ϑ3 ( 2π |iβ) k=−(n−1)/2

X

m m−1/2 )(1+y −1 q m−1/2 ), m=1 (1−q )(1+yq ` −βµ+i k t − βµ − β n L , y2 = e y1 = e , q =e

– ϑ3 (z|τ ) =

Q∞

– – taking β = 2πτ2 → ∞ limit

Snµ =

=

1 h 1−n

n−1/2

∞ Y (1−q m )(1+y1 q m−1/2 )(1+y1−1 q m−1/2 ) 2 i log m−1/2 )(1+y −1 q m−1/2 ) m 2 m=1 (1−q )(1+y2 q k=−(n−1)2

X

∞ i 2 h X (−1)l−1 e −lβµ +e lβµ  l`t  l`t  sin csc −n , lβ(m−1/2) 1−n l,m=1 l 2L 2Ln e

µ Sn=1 =2

∞ X l`t i (−1)l−1 cosh (lβµ) h l`t 1− cot . l sinh (lβ/2) 2L 2L l=1

– valid for y2 q 1/2 , y2−1 q 1/2 < 1 ⇒ −1/2 < µ < 1/2 & S → 0 for β → ∞. – same for other constant µ due to the periodicity S(µ) = S(µ + 1) = S(µ − 1).

EE (µ) for NS-NS sector – NS-NS (a = b = 1/2) for J = τ1 = 0: Snµ =

1 h 1−n

iβµ ϑ[1/2−a−J b−1/2 ](τ1 J + iτ2 µ|τ ) → ϑ3 ( 2π |iβ)

n−1/2

`t ϑ3 ( kn 2πL + iβµ |iβ) 2 i 2π , log iβµ ϑ3 ( 2π |iβ) k=−(n−1)/2

X

m m−1/2 )(1+y −1 q m−1/2 ), m=1 (1−q )(1+yq ` −βµ+i k t − βµ − β n L , y2 = e y1 = e , q =e

– ϑ3 (z|τ ) =

Q∞

– – taking β = 2πτ2 → ∞ limit

Snµ =

=

1 h 1−n

n−1/2

∞ Y (1−q m )(1+y1 q m−1/2 )(1+y1−1 q m−1/2 ) 2 i log m−1/2 )(1+y −1 q m−1/2 ) m 2 m=1 (1−q )(1+y2 q k=−(n−1)2

X

∞ i 2 h X (−1)l−1 e −lβµ +e lβµ  l`t  l`t  sin csc −n , lβ(m−1/2) 1−n l,m=1 l 2L 2Ln e

µ Sn=1 =2

∞ X l`t i (−1)l−1 cosh (lβµ) h l`t 1− cot . l sinh (lβ/2) 2L 2L l=1

– valid for y2 q 1/2 , y2−1 q 1/2 < 1 ⇒ −1/2 < µ < 1/2 & S → 0 for β → ∞. – same for other constant µ due to the periodicity S(µ) = S(µ + 1) = S(µ − 1).

EE (µ) for NS-NS sector – NS-NS (a = b = 1/2) for J = τ1 = 0: Snµ =

1 h 1−n

iβµ ϑ[1/2−a−J b−1/2 ](τ1 J + iτ2 µ|τ ) → ϑ3 ( 2π |iβ)

n−1/2

`t ϑ3 ( kn 2πL + iβµ |iβ) 2 i 2π , log iβµ ϑ3 ( 2π |iβ) k=−(n−1)/2

X

m m−1/2 )(1+y −1 q m−1/2 ), m=1 (1−q )(1+yq ` −βµ+i k t − βµ − β n L , y2 = e y1 = e , q =e

– ϑ3 (z|τ ) =

Q∞

– – taking β = 2πτ2 → ∞ limit

Snµ =

1 h 1−n

=

µ Sn=1 =2

n−1/2

∞ Y (1−q m )(1+y1 q m−1/2 )(1+y1−1 q m−1/2 ) 2 i log m−1/2 )(1+y −1 q m−1/2 ) m 2 m=1 (1−q )(1+y2 q k=−(n−1)2

X

∞ i 2 h X (−1)l−1 e −lβµ +e lβµ  l`t  l`t  sin csc −n , lβ(m−1/2) 1−n l,m=1 l 2L 2Ln e ∞ X l`t i (−1)l−1 cosh (lβµ) h l`t 1− cot . l sinh (lβ/2) 2L 2L l=1

– valid for y2 q 1/2 , y2−1 q 1/2 < 1 ⇒ −1/2 < µ < 1/2 & S → 0 for β → ∞. – same for other constant µ due to the periodicity S(µ) = S(µ + 1) = S(µ − 1).

EE (µ) for NS-NS sector – NS-NS (a = b = 1/2) for J = τ1 = 0: Snµ =

1 h 1−n

iβµ ϑ[1/2−a−J b−1/2 ](τ1 J + iτ2 µ|τ ) → ϑ3 ( 2π |iβ)

n−1/2

`t ϑ3 ( kn 2πL + iβµ |iβ) 2 i 2π , log iβµ ϑ3 ( 2π |iβ) k=−(n−1)/2

X

Q∞ m m−1/2 )(1+y −1 q m−1/2 ), m=1 (1−q )(1+yq ` −βµ+i k t − βµ − β n L , y2 = e y1 = e , q =e

– ϑ3 (z|τ ) =

– – taking β = 2πτ2 → ∞ limit

Snµ =

=

1 h 1−n

n−1/2

∞ Y (1−q m )(1+y1 q m−1/2 )(1+y1−1 q m−1/2 ) 2 i log m−1/2 )(1+y −1 q m−1/2 ) m 2 m=1 (1−q )(1+y2 q k=−(n−1)2

X

∞ i 2 h X (−1)l−1 e −lβµ +e lβµ  l`t  l`t  sin csc −n , lβ(m−1/2) 1−n l,m=1 l 2L 2Ln e

µ Sn=1 =2

∞ X l`t i (−1)l−1 cosh (lβµ) h l`t . 1− cot l sinh (lβ/2) 2L 2L l=1

– valid for y2 q 1/2 , y2−1 q 1/2 < 1 ⇒ −1/2 < µ < 1/2 & S → 0 for β → ∞. – same for other constant µ due to the periodicity S(µ) = S(µ + 1) = S(µ − 1). Ogawa, Takayanagi and Ugajin 2011; Herzog and Nishioka 2013

• Consider β(µ − 1/2) = M = const. for β → ∞ & µ → 1/2 Q (1 − q m )(1 + yq m−1/2 ) (1 + y −1 q m+1/2 ) – ϑ3 (z|τ ) = (1 + y −1 q 1/2 ) ∞ | | {z } m=1 {z } separate contribution for EE validity extended to −1/2 < µ < 3/2 lβ

µ Sn=1 =2

    ∞ X e− 2 l`t (−1)l−1 −Ml l`t e + cot . 1 − l 2L 2L sinh( lβ ) l=1 2

– µ = 1/2: one of the energy levels of the anti-periodic fermion! – red contribution exist for general value M (here M < 1.)

– in general, non-zero contribution exists for    N N = ±1, ±3, ±5, · · · β µ− = const. N = 0, ±2, ±4, · · · 2

anti-periodic fermion, NS periodic fermion, R

– EE (R´ enyi entropy) is useful for probing the energy level!

• Consider β(µ − 1/2) = M = const. for β → ∞ & µ → 1/2 Q (1 − q m )(1 + yq m−1/2 ) (1 + y −1 q m+1/2 ) – ϑ3 (z|τ ) = (1 + y −1 q 1/2 ) ∞ | | {z } m=1 {z } separate contribution for EE validity extended to −1/2 < µ < 3/2 lβ

µ Sn=1 =2

    ∞ X e− 2 l`t (−1)l−1 −Ml l`t e + cot . 1 − l 2L 2L sinh( lβ ) l=1 2

– µ = 1/2: one of the energy levels of the anti-periodic fermion! – red contribution exist for general value M (here M < 1.)

– in general, non-zero contribution exists for    N N = ±1, ±3, ±5, · · · β µ− = const. N = 0, ±2, ±4, · · · 2

anti-periodic fermion, NS periodic fermion, R

– EE (R´ enyi entropy) is useful for probing the energy level!

• Consider β(µ − 1/2) = M = const. for β → ∞ & µ → 1/2 Q (1 − q m )(1 + yq m−1/2 ) (1 + y −1 q m+1/2 ) – ϑ3 (z|τ ) = (1 + y −1 q 1/2 ) ∞ | | {z } m=1 {z } separate contribution for EE validity extended to −1/2 < µ < 3/2 lβ

µ Sn=1 =2

    ∞ X e− 2 l`t (−1)l−1 −Ml l`t e + cot . 1 − l 2L 2L sinh( lβ ) l=1 2

– µ = 1/2: one of the energy levels of the anti-periodic fermion! – red contribution exist for general value M (here M < 1 .)

– in general, non-zero contribution exists for    N N = ±1, ±3, ±5, · · · β µ− = const. N = 0, ±2, ±4, · · · 2

anti-periodic fermion, NS periodic fermion, R

– EE (R´ enyi entropy) is useful for probing the energy level!

• Consider β(µ − 1/2) = M = const. for β → ∞ & µ → 1/2 Q (1 − q m )(1 + yq m−1/2 ) (1 + y −1 q m+1/2 ) – ϑ3 (z|τ ) = (1 + y −1 q 1/2 ) ∞ | | {z } m=1 {z } separate contribution for EE validity extended to −1/2 < µ < 3/2 lβ

µ Sn=1 =2

    ∞ X e− 2 l`t (−1)l−1 −Ml l`t e + cot . 1 − l 2L 2L sinh( lβ ) l=1 2

– µ = 1/2: one of the energy levels of the anti-periodic fermion! – red contribution exist for general value M (here M < 1 .)

– in general, non-zero contribution exists for    N N = ±1, ±3, ±5, · · · β µ− = const. N = 0, ±2, ±4, · · · 2

anti-periodic fermion, NS periodic fermion, R

– EE (R´ enyi entropy) is useful for probing the energy level!

EE (J) • R´enyi entropy derived in the introduction SnJ,µ =

1 h log 1−n

ϑ[1/2−a−J ]( k `t + τ1 J + iτ2 µ|τ ) 2 i b−1/2 n 2πL . 1/2−a−J ϑ[ ](τ J + iτ µ|τ ) 1 2 k=−(n−1)/2 b−1/2 n−1/2

Y

• simple case: a = b = 1/2 & µ = α = 2πτ1 = 0 at β → ∞ limit  P ∞    2 l=1 S=    2 P∞ l=1

(−1)l−1 l sinh(lβ/2)

h

(−1)l−1 l tanh(lβ/2)

h

1− 1−

l`t 2L

cot



l`t 2L

cot



l`t 2L l`t 2L

i

,

J =0

(NS) ,

i

,

J = 12

(R) .

– J = 0 → J = 1/2: visible effects in EE (R´ enyi entropy)! • mode expansion in the presence of the current J X ψ= ψr (t)e i˜r s . ˜ r ∈Z+a+J

– changing J is equivalent to changing a.

EE (J) • R´enyi entropy derived in the introduction SnJ,µ =

1 h log 1−n

ϑ[1/2−a−J ]( k `t + τ1 J + iτ2 µ|τ ) 2 i b−1/2 n 2πL . 1/2−a−J ϑ[ ](τ J + iτ µ|τ ) 1 2 k=−(n−1)/2 b−1/2 n−1/2

Y

• simple case: a = b = 1/2 & µ = α = 2πτ1 = 0 at β → ∞ limit  P ∞    2 l=1 S=    2 P∞ l=1

(−1)l−1 l sinh(lβ/2)

h

(−1)l−1 l tanh(lβ/2)

h

1− 1−

l`t 2L

cot



l`t 2L

cot



l`t 2L l`t 2L

i

,

J =0

(NS) ,

i

,

J = 12

(R) .

– J = 0 → J = 1/2: visible effects in EE (R´ enyi entropy)! • mode expansion in the presence of the current J X ψ= ψr (t)e i˜r s . ˜ r ∈Z+a+J

– changing J is equivalent to changing a.

EE (J) • R´enyi entropy derived in the introduction SnJ,µ =

1 h log 1−n

ϑ[1/2−a−J ]( k `t + τ1 J + iτ2 µ|τ ) 2 i b−1/2 n 2πL . 1/2−a−J ϑ[ ](τ J + iτ µ|τ ) 1 2 k=−(n−1)/2 b−1/2 n−1/2

Y

• simple case: a = b = 1/2 & µ = α = 2πτ1 = 0 at β → ∞ limit  P ∞    2 l=1 S=    2 P∞ l=1

(−1)l−1 l sinh(lβ/2)

h

(−1)l−1 l tanh(lβ/2)

h

1− 1−

l`t 2L

cot



l`t 2L

cot



l`t 2L l`t 2L

i

,

J =0

(NS) ,

i

,

J = 12

(R) .

– J = 0 → J = 1/2: visible effects in EE (R´ enyi entropy)! • mode expansion in the presence of the current J X ψ= ψr (t)e i˜r s . ˜ r ∈Z+a+J

– changing J is equivalent to changing a.

• anti-periodic fermion at small temperature limit: a + J = 1/2 ∞ X

   (−1)l−1 l`t l`t cos([m − 1/2]αl) cos(αJl) × 1 − cot (m−1/2)βl 2L 2L le l,m=1    `t `t = 4e −β/2 cos (α/2) cos(αJ) 1 − cot + ··· 2L 2L

SJ = 4

– EE is a periodic function of J and α. – EE depends on α in two different ways, producing ‘interference pattern’ – Dominant contribution (l = m = 1) has a ‘beat frequency’ J/π for J < 1/2

• periodic fermion at small temperature limit: a + J = 0 ∞ X (−1)l−1 S =2 l l=1 J

"

#    ∞ X l`t l`t cos(mαl) 1+ 2 cos(αJl) × 1 − cot . mβl e 2L 2L m=1

– similar to anti-periodic fermions for temperature dependent parts – at β = ∞, EE has non-zero contributions. – for αJ = π, negative! (there is infinite contribution independent of J)

• anti-periodic fermion at small temperature limit: a + J = 1/2 ∞ X

   (−1)l−1 l`t l`t cos([m − 1/2]αl) cos(αJl) × 1 − cot (m−1/2)βl 2L 2L le l,m=1    `t `t = 4e −β/2 cos (α/2) cos(αJ) 1 − cot + ··· 2L 2L

SJ = 4

– EE is a periodic function of J and α. – EE depends on α in two different ways, producing ‘interference pattern’ – Dominant contribution (l = m = 1) has a ‘beat frequency’ J/π for J < 1/2

• periodic fermion at small temperature limit: a + J = 0 ∞ X (−1)l−1 S =2 l l=1 J

"

#    ∞ X l`t l`t cos(mαl) 1+ 2 cos(αJl) × 1 − cot . mβl e 2L 2L m=1

– similar to anti-periodic fermions for temperature dependent parts – at β = ∞, EE has non-zero contributions. – for αJ = π, negative! (there is infinite contribution independent of J)

Large radius limit, `t /L  1 • NS-NS sector with only chemical potential for simplicity. – ϑ3 (z|τ ) =

Q∞

m=1 (1−q

m ) (1+yq m−1/2 )(1+y −1 q m−1/2 ),

| {z } (1+q 2m−1 +2 cos(2πz2 )q m−1/2 ) – for z1 = i βµ , z2 = i βµ + 2π 2π 1+q

2m−1

+2 cos(2πz2 )q

k `t n L

m−1/2

and `t /L  1

= 1+q − 2q

Snµ =

=

1 h 1−n

2m−1

+2 cos(2πz1 )q

m−1/2 

i

m−1/2

 1 k `t 2 k `t sinh(βµ)+ ( ) cosh(βµ) +· · · . n L 2 n L

n−1/2

∞ Y (1−q m )(1+y1 q m−1/2 )(1+y1−1 q m−1/2 ) 2 i log m−1/2 )(1+y −1 q m−1/2 ) m 2 m=1 (1−q )(1+y2 q k=−(n−1)2

X

 4 ∞ (n + 1)π 2 `2t X 4 + 4 cosh(βµ) cosh(βm) `t +O , 2 2 12n L m=1 (cosh(βm) + cosh(βµ)) L

– linear terms identically 0 upon summing k – similar for all J & µ dependent parts of EE & R´ enyi entropy

Large radius limit, `t /L  1 • NS-NS sector with only chemical potential for simplicity. – ϑ3 (z|τ ) =

Q∞

m=1 (1−q

m ) (1+yq m−1/2 )(1+y −1 q m−1/2 ),

| {z } (1+q 2m−1 +2 cos(2πz2 )q m−1/2 ) – for z1 = i βµ , z2 = i βµ + 2π 2π 1+q

2m−1

+2 cos(2πz2 )q

k `t n L

m−1/2

and `t /L  1

= 1+q

2m−1

+2 cos(2πz1 )q

m−1/2

 1 k `t 2 m−1/2  k `t sinh(βµ)+ ( ) cosh(βµ) +· · · . − 2q i n L 2 n L

Snµ =

=

1 h 1−n

n−1/2

∞ Y (1−q m )(1+y1 q m−1/2 )(1+y1−1 q m−1/2 ) 2 i log m−1/2 )(1+y −1 q m−1/2 ) m 2 m=1 (1−q )(1+y2 q k=−(n−1)2

X

 4 ∞ `t (n + 1)π 2 `2t X 4 + 4 cosh(βµ) cosh(βm) + O , 12n L2 m=1 (cosh(βm) + cosh(βµ))2 L

– linear terms identically 0 upon summing k – similar for all J & µ dependent parts of EE & R´ enyi entropy

Large radius limit, `t /L  1 • NS-NS sector with only chemical potential for simplicity. – ϑ3 (z|τ ) =

Q∞

m=1 (1−q

m ) (1+yq m−1/2 )(1+y −1 q m−1/2 ),

| {z } (1+q 2m−1 +2 cos(2πz2 )q m−1/2 ) – for z1 = i βµ , z2 = i βµ + 2π 2π 1+q

2m−1

+2 cos(2πz2 )q

k `t n L

m−1/2

and `t /L  1

= 1+q

2m−1

+2 cos(2πz1 )q

m−1/2

 1 k `t 2 m−1/2  k `t sinh(βµ)+ ( ) cosh(βµ) +· · · . − 2q i n L 2 n L

Snµ =

=

1 h 1−n

n−1/2

∞ Y (1−q m )(1+y1 q m−1/2 )(1+y1−1 q m−1/2 ) 2 i log m−1/2 )(1+y −1 q m−1/2 ) m 2 m=1 (1−q )(1+y2 q k=−(n−1)2

X

 4 ∞ (n + 1)π 2 `2t X 4 + 4 cosh(βµ) cosh(βm) `t , + O 12n L2 m=1 (cosh(βm) + cosh(βµ))2 L

– linear terms identically 0 upon summing k – Previously EE is independent of µ for an interval in infinite space based on symmetry Cardy, “Entanglement in CFTs at Finite Chemical Potential,” presentation at the Yukawa International Seminar 2016 (YKIS2016) “Quantum Matter, Spacetime and Information.”

– similar for all J & µ dependent parts of EE & R´ enyi entropy

Mutual (R´ enyi) information In (A, B) = Sn (A) + Sn (B) − Sn (A ∪ B) – measuring entanglement between two intervals, `A and `B , separated by `C – free of UV divergence and finite.

• NS-NS sector at zero temperature limit: In = In0 + InJ,µ Inµ (A, B) =

=

2 n−1

(n−1)/2

X k=−(n−1)/2

log

`A +`B + iβµ |iβ) ϑ3 ( iβµ |iβ) 2 2πL 2π 2π ` ` iβµ iβµ A B ϑ3 ( kn 2πL + 2π |iβ) ϑ3 ( kn 2πL + 2π |iβ)

ϑ3 ( kn

 ∞ sin 2 X (−1)l−1 cosh(lβµ) n− n−1 l=1 l sinh(lβ/2) sin

 l(`A +`B )  l`A  sin l`2LB sin 2L 2L − + .   +`B  l `A sin nl `2LB sin nl `A2L n 2L

– for simplicity, α = 2πτ1 = 0, J = 0 and a+J = 1/2, b = 1/2 – dependence on µ (also on J) are the same as R´ nyi entropy & EE – independent of separation `C between two intervals `A and `B .

Mutual (R´ enyi) information In (A, B) = Sn (A) + Sn (B) − Sn (A ∪ B) – measuring entanglement between two intervals, `A and `B , separated by `C – free of UV divergence and finite.

• NS-NS sector at zero temperature limit: In = In0 + InJ,µ Inµ (A, B) =

=

2 n−1

(n−1)/2

X k=−(n−1)/2

∞ X

log

`A +`B + iβµ |iβ) ϑ3 ( iβµ |iβ) 2 2πL 2π 2π ` ` iβµ iβµ A B ϑ3 ( kn 2πL + 2π |iβ) ϑ3 ( kn 2πL + 2π |iβ)

ϑ3 ( kn

 sin 2 (−1)l−1 cosh(lβµ) n− n−1 l=1 l sinh(lβ/2) sin

 l(`A +`B )  l`A  sin l`2LB sin 2L 2L − + .   +`B  l `A sin nl `2LB sin nl `A2L n 2L

– for simplicity, α = 2πτ1 = 0, J = 0 and a+J = 1/2, b = 1/2 – dependence on µ (also on J) are the same as R´ enyi entropy & EE – independent of separation `C between two intervals `A and `B .

Mutual (R´ enyi) information In (A, B) = Sn (A) + Sn (B) − Sn (A ∪ B) – measuring entanglement between two intervals, `A and `B , separated by `C – free of UV divergence and finite.

• NS-NS sector at zero temperature limit: In = In0 + InJ,µ Inµ (A, B) =

=

2 n−1

(n−1)/2

X k=−(n−1)/2

log

`A +`B + iβµ |iβ) ϑ3 ( iβµ |iβ) 2 2πL 2π 2π ` ` iβµ iβµ A B ϑ3 ( kn 2πL + 2π |iβ) ϑ3 ( kn 2πL + 2π |iβ)

ϑ3 ( kn

 ∞ sin 2 X (−1)l−1 cosh(lβµ) n− n−1 l=1 l sinh(lβ/2) sin

 l(`A +`B )  l`A  sin l`2LB sin 2L 2L − + .   +`B  l `A sin nl `2LB sin nl `A2L n 2L

– for simplicity, α = 2πτ1 = 0, J = 0 and a+J = 1/2, b = 1/2 – dependence on µ (also on J) are the same as R´ enyi entropy & EE – independent of separation `C between two intervals `A and `B .

Summary & future directions • Generalized R´enyi & EE in the presence of J and µ • Compute the entropies with J and µ in zero T & large radius limits. – The entropies are periodic in J, which has the role of ‘beat frequency’ – The entropies vanish as fast as O(`t /L)2 – The entropies is non-zero for β(µ − N/2) = const. as β → 0, µ → N/2 • Mutual (R´enyi) information has same dependences on J & µ, which is further independent of the separation between the intervals.

• Future directions : – seeking possible experimental signatures of ‘beat frequency’ – applying this to three dimensional static system .. .

Entanglement Entropy with Current & Chemical Potential

May 7, 2017 - trace over H euclidean time evolution t →t+2πτ2 with H. (twisted B.C. a for s ∼ s + 2π). – s →s−2πτ1 with e−2πiτ1P , P momentum.

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