1. Quantum Computing Are We There Yet?
Emil Khabiboulline
Ph 070: Popular Presentation
Caltech

2. Speedup of 100,000,000!
Announced by Google in December:

3. A Working Quantum Computer?
There certainly is hype… And all the key players are starting to notice

4. Outline The Power of Quantum Great. But Can We Do It?
Ultracold (Atoms)
Ultracold (Wires)
What’s Next?

5. The Power of Quantum 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

6. Moore’s Law
Doubling in computational power every 1.5 years, over the past 50 years

7. Not bits, qubits
Quantum computers also scale exponentially, but in number of qubits, not years What is a quantum bit? =

8. 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)

9. An example: Deutsch’s Problem
Classically:
Compute 𝑓 0
Compute 𝑓 1
Compare 𝑓 0 with 𝑓 1
Requires 2 computations

10. An example: Deutsch’s Problem
Quantumly:
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

11. An example: Deutsch’s Problem

12. 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

13. Other applications (and limitations)
Two major applications:
Generic search / optimization
Quantum simulation
There are tasks where quantum computers are slower
Will not replace your laptop for word processing, browsing the web, etc.

14. Cats: Alive and dead
What do we need?
Great. But Can We Do It?

15. 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

16. What do we need? Interaction with environment leads to “decoherence”
We need exotic conditions:
Very clean for isolation
Very cold for quantum-ness

17. Ultracold (Atoms) Translating math to physics “Atom-like” systems
An example: Trapped ions
Ultracold (Atoms)

18. 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)

19. “Atom-like” systems Broad category: Atoms Ions Quantum dots
Defects in diamond

20. An example: Trapped ions
Harty et al., 2014

21. Superconducting qubits
Google’s quantum computer
Ultracold (Wires)

22. Superconducting qubits
Superconducting circuit consisting of inductor and capacitor Advantages: easy fabrication and handling
Ladd et al., 2010

23. Google’s quantum computer
Google is now using the D-Wave 2X quantum annealer: qubits but not a real quantum computer Already has the Quantum AI Lab Recently hired John Martinis, a leading expert

24. Topological quantum computing
Are we there yet?
What’s Next?

25. Topological quantum computing
“Topological protection” from noise and decoherence Quantum computing by “braiding” particles No physical examples yet… but wait for superconducting wires

26. Maybe But the question is no longer if?, but when?
Are we there yet?
Maybe But the question is no longer if?, but when?