Deconstruction and Conditional Erasure of Correlations Joint work - PowerPoint PPT Presentation

Deconstruction and Conditional Erasure of Correlations Joint work with Mario Berta, Fernando Brandao, and Mark Wilde (arXiv:1609.06994) Christian Majenz QMATH, University of Copenhagen Beyond I.I.D. in Information Theory, National University of Singapore

Introduction: Decoupling and Erasure

Erasure of correlations ◮ Task introduced by Groisman, Popescu and Winter in ’04

Erasure of correlations ◮ Task introduced by Groisman, Popescu and Winter in ’04 ◮ goal: decorrelate two systems by applying local noise

Erasure of correlations ◮ Task introduced by Groisman, Popescu and Winter in ’04 ◮ goal: decorrelate two systems by applying local noise Step-by-step definition:

Erasure of correlations ◮ Task introduced by Groisman, Popescu and Winter in ’04 ◮ goal: decorrelate two systems by applying local noise Step-by-step definition: - bipartite quantum system A ⊗ E in mixed state ρ AE E A

Erasure of correlations ◮ Task introduced by Groisman, Popescu and Winter in ’04 ◮ goal: decorrelate two systems by applying local noise Step-by-step definition: - bipartite quantum system A ⊗ E in mixed state ρ AE - apply random unitary channel E A

Erasure of correlations ◮ Task introduced by Groisman, Popescu and Winter in ’04 ◮ goal: decorrelate two systems by applying local noise Step-by-step definition: - bipartite quantum system A ⊗ E in mixed state ρ AE - apply random unitary channel - correlations erased if approximately product E A

Erasure of correlations ◮ Task introduced by Groisman, Popescu and Winter in ’04 ◮ goal: decorrelate two systems by applying local noise Step-by-step definition: - bipartite quantum system A ⊗ E in mixed state ρ AE - apply random unitary channel - correlations erased if approximately product - how big do we have to choose k ? E A

Erasure of correlations ◮ Task introduced by Groisman, Popescu and Winter in ’04 ◮ goal: decorrelate two systems by applying local noise Step-by-step definition: - bipartite quantum system A ⊗ E in mixed state ρ AE - apply random unitary channel - correlations erased if approximately product - how big do we have to choose k ? - optimal: k ≈ nI ( A : E ) σ for ρ = σ ⊗ n E A

Erasure of correlations ◮ Task introduced by Groisman, Popescu and Winter in ’04 ◮ goal: decorrelate two systems by applying local noise Step-by-step definition: - bipartite quantum system A ⊗ E in mixed state ρ AE - apply random unitary channel - correlations erased if approximately product - how big do we have to choose k ? - optimal: k ≈ nI ( A : E ) σ for ρ = σ ⊗ n ⇒ Operational interpretation of the quantum mutual information!

Erasure of correlations ◮ Different erasure model: partial trace (aka decoupling, Horodecki, Oppenheim and Winter ’05)

Erasure of correlations ◮ Different erasure model: partial trace (aka decoupling, Horodecki, Oppenheim and Winter ’05) ◮ Ubiquitous proof tool (quantum Shannon theory, thermodynamics etc.)

Erasure of correlations ◮ Different erasure model: partial trace (aka decoupling, Horodecki, Oppenheim and Winter ’05) ◮ Ubiquitous proof tool (quantum Shannon theory, thermodynamics etc.) Step-by-step definition: - bipartite quantum system A ⊗ E in mixed state ρ AE E A

Erasure of correlations ◮ Different erasure model: partial trace (aka decoupling, Horodecki, Oppenheim and Winter ’05) ◮ Ubiquitous proof tool (quantum Shannon theory, thermodynamics etc.) Step-by-step definition: - bipartite quantum system A ⊗ E in mixed state ρ AE - divide A ∼ = A 1 ⊗ A 2 E A 1 A 2

Erasure of correlations ◮ Different erasure model: partial trace (aka decoupling, Horodecki, Oppenheim and Winter ’05) ◮ Ubiquitous proof tool (quantum Shannon theory, thermodynamics etc.) Step-by-step definition: - bipartite quantum system A ⊗ E in mixed state ρ AE - divide A ∼ = A 1 ⊗ A 2 - apply a unitary to A E A 1 A 2

Erasure of correlations ◮ Different erasure model: partial trace (aka decoupling, Horodecki, Oppenheim and Winter ’05) ◮ Ubiquitous proof tool (quantum Shannon theory, thermodynamics etc.) Step-by-step definition: - bipartite quantum system A ⊗ E in mixed state ρ AE - divide A ∼ = A 1 ⊗ A 2 - apply a unitary to A - trace out A 2 ⇒ approximate product state A 2 E A 1

Erasure of correlations ◮ Different erasure model: partial trace (aka decoupling, Horodecki, Oppenheim and Winter ’05) ◮ Ubiquitous proof tool (quantum Shannon theory, thermodynamics etc.) Step-by-step definition: - bipartite quantum system A ⊗ E in mixed state ρ AE - divide A ∼ = A 1 ⊗ A 2 - apply a unitary to A - trace out A 2 ⇒ approximate product state - how big do we have to choose A 2 ? A 2 E A 1

Erasure of correlations ◮ Different erasure model: partial trace (aka decoupling, Horodecki, Oppenheim and Winter ’05) ◮ Ubiquitous proof tool (quantum Shannon theory, thermodynamics etc.) Step-by-step definition: - bipartite quantum system A ⊗ E in mixed state ρ AE - divide A ∼ = A 1 ⊗ A 2 - apply a unitary to A - trace out A 2 ⇒ approximate product state - how big do we have to choose A 2 ? 2 I ( A : E ) σ for ρ = σ ⊗ n (Horodecki, Oppenheim, - log | A 2 | ≈ n Winter ’05)

Erasure of correlations ◮ Different erasure model: partial trace (aka decoupling, Horodecki, Oppenheim and Winter ’05) ◮ Ubiquitous proof tool (quantum Shannon theory, thermodynamics etc.) Step-by-step definition: - bipartite quantum system A ⊗ E in mixed state ρ AE - divide A ∼ = A 1 ⊗ A 2 - apply a unitary to A - trace out A 2 ⇒ approximate product state - how big do we have to choose A 2 ? 2 I ( A : E ) σ for ρ = σ ⊗ n (Horodecki, Oppenheim, - log | A 2 | ≈ n Winter ’05) ! Erasure models ar related, exact one shot equivalence if ancillary states are allowed

This talk Erasure of correlations E A 1 Deconstruction A 2 A 1 E R A 2 Conditional Erasure A 1 E R A 2

Erasure of conditional correlations

Conditional correlations ◮ ρ AER

Conditional correlations ◮ ρ AER ◮ Conditional quantum mutual information I ( A : E | R ) ρ = H ( ρ AR ) + H ( ρ ER ) − H ( ρ AER ) − H ( ρ R )

Conditional correlations ◮ ρ AER ◮ Conditional quantum mutual information I ( A : E | R ) ρ = H ( ρ AR ) + H ( ρ ER ) − H ( ρ AER ) − H ( ρ R ) ◮ Recoverability: if I ( A : E | R ) = ε small, ρ AER ≈ O ( ε ) R R → RA ( ρ ER ) for some quantum channel R . (Fawzi, Renner ’14)

Conditional correlations ◮ ρ AER ◮ Conditional quantum mutual information I ( A : E | R ) ρ = H ( ρ AR ) + H ( ρ ER ) − H ( ρ AER ) − H ( ρ R ) ◮ Recoverability: if I ( A : E | R ) = ε small, ρ AER ≈ O ( ε ) R R → RA ( ρ ER ) for some quantum channel R . (Fawzi, Renner ’14) R E A

Conditional correlations ◮ ρ AER ◮ Conditional quantum mutual information I ( A : E | R ) ρ = H ( ρ AR ) + H ( ρ ER ) − H ( ρ AER ) − H ( ρ R ) ◮ Recoverability: if I ( A : E | R ) = ε small, ρ AER ≈ O ( ε ) R R → RA ( ρ ER ) for some quantum channel R . (Fawzi, Renner ’14) R E

Conditional correlations ◮ ρ AER ◮ Conditional quantum mutual information I ( A : E | R ) ρ = H ( ρ AR ) + H ( ρ ER ) − H ( ρ AER ) − H ( ρ R ) ◮ Recoverability: if I ( A : E | R ) = ε small, ρ AER ≈ O ( ε ) R R → RA ( ρ ER ) for some quantum channel R . (Fawzi, Renner ’14) R E A

Conditional correlations ◮ ρ AER ◮ Conditional quantum mutual information I ( A : E | R ) ρ = H ( ρ AR ) + H ( ρ ER ) − H ( ρ AER ) − H ( ρ R ) ◮ Recoverability: if I ( A : E | R ) = ε small, ρ AER ≈ O ( ε ) R R → RA ( ρ ER ) for some quantum channel R . (Fawzi, Renner ’14) R E A

Conditional correlations ◮ ρ AER ◮ Conditional quantum mutual information I ( A : E | R ) ρ = H ( ρ AR ) + H ( ρ ER ) − H ( ρ AER ) − H ( ρ R ) ◮ Recoverability: if I ( A : E | R ) = ε small, ρ AER ≈ O ( ε ) R R → RA ( ρ ER ) for some quantum channel R . (Fawzi, Renner ’14) ⇒ All correlations of A and E mediated by R

Conditional correlations ◮ ρ AER ◮ Conditional quantum mutual information I ( A : E | R ) ρ = H ( ρ AR ) + H ( ρ ER ) − H ( ρ AER ) − H ( ρ R ) ◮ Recoverability: if I ( A : E | R ) = ε small, ρ AER ≈ O ( ε ) R R → RA ( ρ ER ) for some quantum channel R . (Fawzi, Renner ’14) ⇒ All correlations of A and E mediated by R ⇒ E − R − A is approximate quantum Markov chain

Conditional correlations ◮ ρ AER ◮ Conditional quantum mutual information I ( A : E | R ) ρ = H ( ρ AR ) + H ( ρ ER ) − H ( ρ AER ) − H ( ρ R ) ◮ Recoverability: if I ( A : E | R ) = ε small, ρ AER ≈ O ( ε ) R R → RA ( ρ ER ) for some quantum channel R . (Fawzi, Renner ’14) ⇒ All correlations of A and E mediated by R ⇒ E − R − A is approximate quantum Markov chain ◮ I ( A : E | R ) measures conditional correlations

Erasure of conditional correlations ◮ i.i.d. setting

Erasure of conditional correlations ◮ i.i.d. setting ◮ Recall: Erasure of correlations in ρ AE operating on A costs I ( A : E ) bits of noise.

Erasure of conditional correlations ◮ i.i.d. setting ◮ Recall: Erasure of correlations in ρ AE operating on A costs I ( A : E ) bits of noise. ? Can we erase conditional correlations by injecting I ( A : E | R ) ρ bits of noise into A ?