From Einstein To Quantum Cryptography

AUC Open Day January 14, 2012

Sebastian de Haro

• First bank transfer encoded via quantum crypto for entangled photons

• Information via glass fiber cable from Vienna City Hall to Bank Austria Creditanstalt branch office “Schottengasse”

Particles or waves?

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http://russherman.com/Talks/FirstThreeMinutes_CollegeDay.pdf AUC Open Day January 14, 2012. SdH

AUC Open Day January 14, 2012. SdH

AUC Open Day January 14, 2012. SdH

AUC Open Day January 14, 2012. SdH

AUC Open Day January 14, 2012. SdH

AUC Open Day January 14, 2012. SdH

Traveling wave Frequency (and velocity) well-defined

Position ill-defined

Wave pulse Position well-defined

Frequency (and velocity) ill-defined

Δ𝑥Δ𝑣 ≥ ℎ/𝑚

Planck’s constant: ℎ = 6,626068 × 10−34 kg m2/s

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“God does not play dice”

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Determinism: “I would always be able to keep my

deterministic faith for fundamental phenomena” (Lorentz)

Causality Can compute, but what does it mean? “If I am not

satisfied with current state of problem it is because I do not understand yet physical meaning of its solution. What Heisenberg has said is mathematically unexceptionable, but the point in question is that of physical interpretation” (Schrödinger).

“Anschaulichkeit”: “The way Dirac has formulated

Schrödinger’s theory [leads to] a more advanced renunciation of Anschaulichkeit, a fact very characteristic of symbolic methods in quantum theory” (Bohr).

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𝑣 = 𝑣1 + 𝑣2 = 0

𝑣1 𝑣2

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𝑣1 = 100 m/s 𝑣2

𝑥 = 𝑥1 + 𝑥2 = 0 𝑣 = 𝑣1 + 𝑣2 = 0

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𝑣1 = 100 m/s 𝑣2

𝑣 = 𝑣1 + 𝑣2 = 0

• No influences faster than light. • Conclusion: particle must have

velocity before we measure it. • Violation of • Therefore quantum mechanics is

an incomplete theory.

Δ𝑥Δ𝑣 ≥ ℎ/𝑚

Faster-than-light interaction is not needed. We only have correlations.

Entanglement: particles correlated and system behaves as a whole rather than sum of parts.

Bell’s theorem (‘64): If independent particles had defined velocities before measured, this implies certain inequality which QM violates.

Experiment confirms quantum mechanics (Aspect ‘82).

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EPR with spin:

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↓ ↑ +

Four possible states:

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1

2↑↓+↓↑

↑↑

1

2↑↓−↓↑

↓↓

𝑠 = 1

𝑠 = 0

Record: 144 km in La Palma, Tenerife

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Big Questions in Science, fall 2011. SdH, AUC 19

Share a randomly generated key

↑= 1 ↓= 0

1

2↑↓−↓↑

110100010 110100010

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Can be used for secure communication. Eavesdropper destroys correlations.

Photons:

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Interference means change No possible ‘unvisible’ eavesdropper Applications:

Banking

Confident information

Collaboration fundamental research with industry (and government).

Key feature: entanglement (“spooky action at a distance”)

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Counter-intuitive aspects: “If you are not confused by quantum physics then you

haven’t really understood it.” (Niels Bohr) “I think I can safely say that nobody understands

quantum mechanics.” (Richard Feynman). After WWII: “Shut up and calculate”. Imposed by increasing numbers of students: “Such

classroom numbers, Berkeley’s department chair exclaimed to his dean, were ‘a disgrace and should not be tolerated at any respectable university’… The larger the class, the less time spent talking through the big issues.” (David Kaiser)

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Central to most of modern physics.

Key experiments and formalism.

Interpretation.

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