Quantum Information: Quantum Mechanics SecondYouth

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Quantum Information Quantum Mechanics
SecondYouth

• Quantum Entanglement
• Quantum Noise

Fabio Benatti, Roberto
Floreanini Dipartimento di Fisica
Teorica, INFN
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The Group at DFT

• Petra SCUDO (Post Doc, DFT)
• Sebastiano ANDERLONI (dottorando UniTs)
• Alexandra LIGUORI (dottoranda UniTs)
• Adam NAGY (dottorando TU Budapest)
• Ugo MARZOLINO (dottorando UniTs)
• Pierfrancesco ROSINI (Laureato 2008)
• Giovanni MORAS (Laureato 2008)
• Giangiacomo GUERRESCHI (Laureando 2008)
• Mauro TONON (Laureando 2008)

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Quantum Informationfrom bits to qubits

• Bits 0,1
• Qubits

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IN THE QUANTUM WORLD STRANGE THINGS HAPPEN
THE QUANTUM SKIER
(Charles Addams)
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Quantum Entanglement

• Alice and Bob share 2 qubits in
• Separable states
• Entangled States

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Quantum Entanglement an epistemological riddle

• Einstein-Podolski-Rosen An entangled
  wavefunction does not describe the physical
  reality in a complete way
• Schroedinger For an entangled state the best
  possible knowledge of the whole does not include
  the best possible knowledge of its parts
• Mermin a correlation that contradicts the theory
  of elements of reality
• Peres a trick that quantum magicians use to
  produce phenomena that cannot be imitated by
  classical magicians

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Quantum Entanglement from Magic to a Physical
Resource

• Bell a correlation that is stronger than any
  classical correlation
• Bennett a resource that enables quantum
  teleportation
• Shor a global structure of the wavefunction
  that allows for faster algorithms
• Ekert a tool for secure communication

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Quantum Noise

• Reversible Quantum Time Evolution
• vector states remain vector
  states
• Irreversible Quantum Time Evolution
• vector states turned into
  mixtures

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Open Quantum Systems

• Quantum systems immersed in their environment

E
S
Dissipation
affected by
Noise
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Open Quantum Systems and Noise

• Decoherence interference effects eliminated
• Extremely useful to derive the classical
  macrodynamics from the quantum microdynamics
  (Ghiradi-Rimini-Weber)
• Extremely dangerous in quantum information and
  computation based on persistence of linear
  superpositions

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Noise can also entangle

• non-directly interacting quantum systems in a
  same environment may interact through the
  environment and become entangled

E
S1
S2
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A Theoretical and Experimental Scenario
Bose-Einstein Condensates (BEC)

• Laser cooling
• Magnetic trapping
• Evaporative cooling
• Rubidium-87 atoms condensed
• at the temperature of
• in 1D wells of width

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50 nK
200 nK
400 nK
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BEC in Double Well Traps
Atom Chips
Noise on the tunneling barrier
BEC Entangled States
Well 1 K atoms
Well 2 N-K atoms
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What are the effects of the environment?It
decoheres, but not only. On short times,

• It can generate a current in an otherwise
  insulating state (poster S. Anderloni)
• it can generate entanglement in an otherwise
  separable state (poster A.M. Liguori)
• It can measurably alter transmission
• and reflection coefficients (poster G.
  Moras)
• it allows to study the wave packet reduction in
  an almost mesoscopic context currently under
  study together with the experimental group of M.
  Inguscio at LENS (Florence)