Quantum Computing

Presented by:Don DavisPHYS 330511-20-2008

Outline

• Bits• Classical Computing• Qubits• Quantum Computing• Conclusion

Bits

• “Binary Digits”– Represented by two distinguishable states

– 0/1– 0V/+5V– Down/Up– On/Off

– May be either of two distinct values corresponding to 0 or 1.• 0V could correspond to 0• +5V could correspond to 1

– Only these two values or states are possible

• Each series of bits can contain one piece of information.– In a 4 bit series: 00000, 00011, 00102, and so on…

Classical Computing

• Logical device(s) in which inputs are converted into a specific output based on user defined programming.

• “Serial” by nature– Each bit, or a small series of bits (typically 32), is processed one

chunk at a time.– Parallel computing can only be accomplished by using more than one

processor at a time.• Computing speed is related to the delay of each logical

operation and by the total number of processors at a linear rate.– A classical computer can compute x number of calculations at once,

where x is the number of processors in use.• 2 classical processors compute twice as fast as 1.

• Advantage: System always outputs the answer based on logic.

Qubits

• “Quantum Binary Digits”– Represented by a two state system, much like the classical

bit.• Positive or negative spin of a particle or energy levels E1 and E2

could represent 0’s and 1’s

– Each qubit may be 0 or 1 or any linear combination of 0 and 1.• A qubit has the ability to store any number of 0’s and 1’s in

superposition.

– One bit can be either 0 or 1.• One qubit can be any combination of a0 + b1, where a and b are

integers.

Two Digit Bit vs. Two Digit Qubit

Bit 1 Bit 2 Decimal Equivalent

0 0 0

0 1 1

1 0 2

1 1 3

Qubit 1 Qubit 2 Decimal Equivalent

0 and/or 1 0 and/or 1 0, 1, 2, and 3

Quantum Computing

• Logical device(s) in which inputs are converted into a specific output based on user defined programming.

• “Parallel” by nature– Each qubit can contain both a 1 and a 0.– All qubits are processed at the same time.

• Computational speed is related to the number of bits in the computer at an exponential rate of base 2.– A quantum computer can compute 2X calculations at once, where x is

the number of bits.• A 2 qubit processor can compute 4 times faster than a 1 qubit processor.• See 0+1, and 1+1 on the board using a 1 qubit quantum computer and 1 bit

classical computer.

• Disadvantage: System always outputs the answer based on probabilities – this may not be the logical equivalent.

Conclusion

• Quantum computers can be compared to classical computers in that they both make use of simple logic operations applied to inputs of 0’s and 1s’.

• Classical computers use bits – 1 or 0– Serial processing

• Quantum computers use qubits – 1 and 0– Parallel processing