# CNOT gate

1. Aug 25, 2004

### Mk

Yeah so, scientists in Japan have the CNOT gate, control not. What does it do? What's the truth table... other stuff. Are gates made of transistors?

2. Aug 26, 2004

### chroot

Staff Emeritus
Could you please provide some context? I have no idea what you're talking about.

- Warren

3. Aug 26, 2004

### cronxeh

Last edited by a moderator: Apr 21, 2017
4. Aug 26, 2004

### marlon

Mk, is talking about Quantum-Information-Technology, chroot. The CNOT gate is one of them reversible gates, and it is also named the reversible XOR-gate. Basically the gate flips the second bit if the first is 1 and does nothing if the first bit is zero (hence the name controlled-not).

This gate performs a NOT on the second bit if the first bit is set to 1 and it performs a copy-operation if the second bit is initially set to 0.

The problem is that all these one-bit and twobit gates are non-universal, they cannot compute any operation using just the gate in question. The "first" universal gate is the three-bit Toffoli-gate or the controlled-controlled-NOT-gate.

It computes : (x,y,z) ---->(x,y,z + xy) where the sum is the sum modulo 2

This gate performs all the operations (NAND, COPY) necessary to be universal...

regards
marlon

5. Aug 26, 2004

### Mk

Thanks a lot. Exactly what I needed... but I'm not sure about the CNOT is the XOR. XOR aka EOR (eyore, the donkey!), is eXclusive OR. XOR gives a true if either A and B but not both, are true.

6. Aug 26, 2004

### marlon

The CNOT gate is just the same as the reversible XOR-gate

regards
marlon

7. Aug 26, 2004

Ahhh! I see.