Transcript Khabiboulline30Popx - Caltech High Energy Physics

Quantum Computing
Are We There Yet?
Emil Khabiboulline
[email protected]
Ph 070: Popular Presentation
05/10/2016 @ Caltech
Speedup of 100,000,000!
Announced by Google in December:
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A Working Quantum Computer?
There certainly is hype…
And all the key players are starting to notice
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Outline
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The Power of Quantum
Great. But Can We Do It?
Ultracold (Atoms)
Ultracold (Wires)
What’s Next?
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Moore’s Law
Not bits, qubits
An example: Deutsch’s Problem
How to break into your bank
Other applications (and limitations)
THE POWER OF QUANTUM
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Moore’s Law
Doubling in computational power every 1.5
years, over the past 50 years
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Not bits, qubits
Quantum computers also scale
exponentially, but in number of qubits, not
years
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What is a quantum bit?
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An example: Deutsch’s Problem
You have some function that takes in 0 or 1
and spits out 0 or 1
You want to know 𝑓 0 ≟ 𝑓(1)
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An example: Deutsch’s Problem
Classically:
1. Compute 𝑓 0
2. Compute 𝑓 1
3. Compare 𝑓 0 with 𝑓 1
Requires 2 computations
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An example: Deutsch’s Problem
Quantumly:
1. Compute directly 𝑓 0 ≟ 𝑓(1)
Requires 1 computation
However, we don’t get to know 𝑓 0 or 𝑓 1
Not magic, just clever use of superposition
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An example: Deutsch’s Problem
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How to break into your bank
RSA encryption works because factoring
large numbers is really hard: exponential
scaling
For quantum computers, the scaling is
polynomial
An example: 300 digit number
Classical: >100 years
Quantum: 1 minute
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Other applications
(and limitations)
Two major applications:
1. Generic search / optimization
2. Quantum simulation
There are tasks where quantum computers
are slower
Will not replace your laptop for word
processing, browsing the web, etc.
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Cats: Alive and dead
What do we need?
GREAT. BUT CAN WE DO IT?
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Cats: Alive and dead
Superpositions are used all the time in
quantum computation: Schrodinger cat state
|0 > +|1 >, True and false,
However, we never see Schrodinger cats in
our lives
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What do we need?
Interaction with environment leads to
“decoherence”
We need exotic conditions:
1. Very clean for isolation
2. Very cold for quantum-ness
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Translating math to physics
“Atom-like” systems
An example: Trapped ions
ULTRACOLD (ATOMS)
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Translating math to physics
Qubit = vector → physical observable (e.g.,
energy) that can be in two states
Quantum gate = matrix → physical process
that acts in different ways depending on the
qubit’s state (e.g., electric field)
Measurement = dot product → physical
measurement (e.g., photon detection)
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“Atom-like” systems
Broad category:
• Atoms
• Ions
• Quantum dots
• Defects in diamond
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An example: Trapped ions
Harty et al., 2014
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Superconducting qubits
Google’s quantum computer
ULTRACOLD (WIRES)
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Superconducting qubits
Superconducting circuit consisting of
inductor and capacitor
Advantages: easy fabrication and handling
Ladd et al., 2010
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Google’s quantum computer
Google is now using the D-Wave 2X
quantum annealer: 1000+ qubits but not a
real quantum computer
Already has the Quantum AI Lab
Recently hired John Martinis, a leading
expert
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Topological quantum computing
Are we there yet?
WHAT’S NEXT?
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Topological quantum computing
“Topological protection”
from noise and
decoherence
Quantum computing by
“braiding” particles
No physical examples
yet… but wait for
superconducting wires
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Are we there yet?
Maybe
But the question is no longer if?, but when?
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