Ordinary Computer 
Adiabatic Circuits 
Quantum Computer 

Goal 
Get 'er done! 
Substantially lower power use, especially at low clockrate. 
Speedups up to exponential: e.g., search n values in sqrt(n) time 
Data storage 
1's and 0's (bits) 
1's and 0's (bits) 
Vector with axes 1 and 0 (qubits) Not just 1 or 0: both at once! 
Assignments? 
Yes 
No (uses energy = kT ln 2) 
No (violates laws of physics) 
Reversible? 
No 
Yes 
Yes, except for "collapse" operation 
Swap? 
Yes 
Yes 
Yes 
Logic gates  AND, OR, NOT  NOT, CNOT, CCNOT 
CNOT, Hadamard rotate 45 degrees 
Programming Model 
Instructions 
Reversible Instructions 
Reversible Quantum Operations, and Irreversible Collapse 
Clock 
Square wave 
Two trapezoidal waves 
Limited by coherence time 
When? 
Now 
Slowly, over next ten years 
??? 
Limits 
Heat/power, hard problems 
Only helps at low clockrate 
How many bits can you keep coherent? 
Small things, like electrons, display several very odd mechanical
properties with mystical sounding "quantum" names: