1. Quantum Computing Presented by: Don Davis PHYS 3305 11-20-2008

2. Outline Bits Classical Computing Qubits Quantum Computing Conclusion

3. 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: 0000  0, 0001  1, 0010  2, and so on…

4. 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.

5. 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 E 1 and E 2 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.

6. Two Digit Bit vs. Two Digit Qubit Bit 1Bit 2Decimal Equivalent 000 011 102 113 Qubit 1Qubit 2Decimal Equivalent 0 and/or 1 0, 1, 2, and 3

7. 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 2 X 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.

8. 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