# Is their a way to perfectly clone coherent state and squeezed states?

Coherent state and squeezed states can be swapped why cloning coherent states can't be perfect to clone we obtain $$|\cos(|z|)b\rangle \otimes |\sin(|z|)b\rangle,$$

If we set $$|z| = \pi/4$$ then

$$|b\rangle \otimes |0\rangle = |b/\sqrt 2\rangle \otimes |b/\sqrt 2\rangle$$

which is imperfect cloning is there a way to perfectly clone?

The no-cloning theorem states that an unknown quantum state cannot be copied exactly --- so this rules out any algorithm that attempts to produce perfect copies of an arbitrary quantum state (including squeezed and coherent states).

As you note, however, the no-cloning theorem does not rule out the production of approximate quantum state clones. Andersen et al. introduced the most-optimal scheme for cloning of Gaussian states --- their algorithm produces a clone with fidelity of 65% to the original state (the proven optimum possible is $$f=2/3$$).

The circuit they use in their algorithm is here: and can be implemented using Strawberry Fields like so:

# state to be cloned
Coherent(0.7+1.2j) | q

# 50-50 beamsplitter
BS = BSgate(pi/4, 0)

# symmetric Gaussian cloning scheme
BS | (q, q)
BS | (q, q)
MeasureX | q
MeasureP | q
Xgate(scale(q, sqrt(2))) | q
Zgate(scale(q, sqrt(2))) | q

# after the final beamsplitter, modes q and q
# will contain identical approximate clones of the
# initial state Coherent(0.1+0j)
BS | (q, q)


You can check out the Gaussian cloning tutorial in the Strawberry Fields documentation for more information.

• Thank you It's really helpful. – pahuldeep singh Sep 20 '19 at 18:20