Transcript FOI2013Posterx

Quantum and classical photon correlation in
four wave mixing and CARS spectroscopy
Rafi Z. Vered, Yelena Ben-Or, Michael Rosenbluh and Avi Pe’er
Department of Physics and BINA Center for Nano-technology, Bar-Ilan University, Ramat-Gan 52900, Israel
Abstract: We demonstrate two-photon interference with correlated photon pairs produced by
FWM. We explore the quantum-classical transition of the light by observing the loss dependence
of the interference contrast for various pump intensities.
Experimental concept:
Introduction:
In degenerate
(FWM), a pump field at frequency 𝜔𝑝 is
converted through a third-order non linearity, to another pair of
frequencies 𝜔𝑠 , 𝜔𝑖 (signal and idler) so that energy and momentum are
conserved 2𝜔𝑝 = 𝜔𝑠 + 𝜔𝑖 , 2𝑘𝑝 ≈ 𝑘𝑠 + 𝑘𝑖 .
p

i
 3
s
p
p
p
i
s
The pump, signal and idler relative phase
relationship (𝜙𝑡𝑜𝑡𝑎𝑙 = 𝜙𝑠 + 𝜙𝑖 − 2𝜙𝑝 ) dictate the direction of energy
flow (from pump to signal/idler light or vice versa).
idler
signal
For 𝜙𝑡𝑜𝑡𝑎𝑙 = 0
For 𝜙𝑡𝑜𝑡𝑎𝑙 = 𝜋
the energy flows from the pump to signal and idler.
the energy flows from signal and idler to pump.
Dispersive window
st
1
nd
2
FWM
s
p
A dispersive window imposes a spectrally modulated relative phase,
causing interference fringes to appear on the FWM spectrum.
, FWM is an amplification process, and its fringe contrast is
expected to be tanh 𝑔, where the gain 𝑔 is dictated by the pump
intensity during the 2nd FWM pass.
, this two-photon interference can reveal the
quantum nature of the signal-idler light in a simple way.
Pump beam Two-photon
BS
Pump Laser
Ti:Sapphire
Two-photon
BS
𝜑 𝜔
0
FWM beam
Experimental setup:
FWM
i
Isolator
Dispersive window
2nd attenuator
6ps pump pulses at 784nm enter a 12 cm long photonic crystal fiber (PCF),
1st attenuator
with zero dispersion at 783nm, generating signal-idler pairs over a broad
frequency range. After the first pass through the fiber the pump and the
PCF
signal-idler pairs are reflected back for a second pass through the fiber. In
Dichroic BS
Spectrometer
between, a dispersive window modulates the spectral phase of the signalClassically,
these
two
scenarios
are
equivalent,
but
quantum
idler pairs compared to the pump, causing the appearance of spectral
mechanically,
they
are
very
different,
as
pump
attenuation
before
the
first
fringes. The resulting FWM spectrum is measured on a high resolution
FWM
reduces
the
bi-photon
flux,
but
leaves
their
correlations
intact,
spectrometer.
whereas attenuation between the passes (loss) hampers the correlation
: attenuating the pump before the fiber.
severely. Thus, the fringe contrast in the first scenario is considerably
: attenuating the pump and FWM between the
higher than in the second scenario, providing a measure of the nonpasses.
classicality of the light.
Results:
Fringe contrast
1
Signal spectrum
(attenuation between passes)
~0%
5%
10%
15%
~0%
5%
10%
15%
0.8
Contrast
Signal spectrum
(attenuation before the fiber)
0.6
0.4
attenuation before the fiber
attenuation between the passes
0.2
0
680
700
720
740
680
700
720
740
(a) Measured spectral interference when attenuation is applied before
the fiber. (b) The same interference when attenuation is applied
between the passes through the fiber. Both graphs present the same
four measurable lowest pump intensities.
0
50
Pump Intensity (mW)
100
150
The measured fringe contrast as a function of the pump power after the 2nd
pass scanned down from 150mW (average power) in two ways, either by
attenuating the pump before both passes (red) or by attenuation between the
passes (blue). Up to 60mW pump power (close to the calculated value, due to
time correlation measurements[1])
, marking the transition between the quantum regime of
single bi-photons at low pump powers and the multi-photon semi-classical
regime at high powers.
[1] Rafi Z. Vered, Michael Rosenbluh, and Avi Pe’er, "Two-photon correlation of broadbandamplified spontaneous four-wave mixing", Phys. Rev. A 86, 043837 (2012).
A simple two-photon interference method has been demonstrated for investigating the quantum correlation of broadband bi-photons
generated by FWM. Due to the high gain of our PCF fiber, we fully observe the transition between quantum and classical regimes. The collinear, in
fiber arrangement makes the experimental configuration inherently robust to phase fluctuations and does not require any phase locking to
observe a stable fringe pattern, thereby considerably simplifying the measurement. We expect this method to be useful as an additional tool in
the quantum optics and quantum information toolbox.