Is photon a wave packet ?

[Qiang Lu <luqiang@NANKAI.EDU.CN>]

Hello friends,

> I have two questions.
> One, if a single photon has the property of wave?
The single photon means an excited atom emits a single photon.
> Two, if a single photon is a wave packet? i.e. if a single photon has
> a width of frequency, but not monochromatic?
In quantum field theory

                    2
            /       _
            |       \
A_{\mu}(x)= | d^3 k /  (a_{k,i} A_{\mu}(k,i;x) + a*_{k,i} A*_{\mu}(k,i;x)
            |       -
           /       i=1

Here creation operator a_{k,i} creats an single photon with
polarization i and frequency k. Thus for a single photon, it must be
absolutely monochromatic. While for wave packet, it is a fourier
expansion of variable frequency, may be k+-dk. For a wave packet the
frequency has a width dk, but not a define and single freqency.
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                   k-dk    k      k+dk
 From this point of wiew, one may say that a single photon is not a
packet. That is why I asked if a single photon is a wave packet?



--
Best regards,
 Qiang