Quantum Computing, Explained

Jim Garrison

Coloft (Santa Monica)

September 29, 2012

Quantum computing is something to be excited about.

Unique features of quantum physics

Although it may not seem believable, this is how the world really works!

Classical and quantum computation

Classical computing
(in a nutshell)

One classical bit

Many classical bits

Classical operations

From here we could build up all of classical computing. We just need more bits.

Onward, to quantum computing!

One quantum bit (“qubit”)

But there's a catch!

Measurement (one qubit)

Measurement (one qubit)

Given one quantum bit, only one classical bit of information can be extracted.

Many quantum bits

Six quantum bits

300 quantum bits

Measurement (many qubits)

Measurement (many qubits)

Partial measurement

Quantum measurement: summarized

Quantum entanglement

Quantum operations

Single qubit operations

“Bloch Sphere” by “Smite-Meister.” Licensed CC-BY-SA from Wikipedia.




NOT: many qubits

Phase: many qubits


Quantum computing must be reversible

Presumably we are working on information at the fundamental level the universe uses to operate.

How to build a quantum computer

DiVincenzo Criteria

Possible hardware implementations

State of the art:
factoring 21 = 3 * 7

Other concepts

Quantum computing is something to be excited about.

Further reading

Note: the language of quantum mechanics is linear algebra (matrices) over the complex numbers