source used, meaning that it will preserve any
degree of second-order correlations present
in the original system. Moreover, the excel-
lent mode quality inherent to the system may
facilitate its efficient interconnection with
other quantum devices ( 2 ). These advantages,
along with the unparalleled performance
of ARR-PCFs, provides a route for multiple
technological applications in fields such as
quantum-enhanced imaging ( 30 ) and com-
munications ( 1 ).
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ACKNOWLEDGMENTS
We thank M. V. Chekhova and C. Genes for useful discussions.
Funding:Max-Planck Society (R.T., J.H., N.Y.J., P.S.J.R., D.N.).
Author contributions:Conceptualization: D.N., N.Y.J., P.S.J.R.SCIENCEscience.org 6 MAY 2022¥VOL 376 ISSUE 6593 623
Original biphotons
(1425 & 849 nm)Up-shifted biphotons
(894 & 849 nm)02468101214–0.6 –0.4 –0.2 0 0.2 0.4 0.6
Time τ (ns)Original biphotons
(1425 & 849 nm)02468101214Time τ (ns)Normalized g(2)
(
τ)Normalized g(2)
(
τ)Normalized g(2)
(
τ)–6 –4 –2 024 6Up-shifted biphotons
(894 & 849 nm)02468101214–6 –4 –2 024 6
Time τ (ns)ABCFig. 4. Unaffected quantum correlations.(A) Second-order correlations of
the original biphoton pairs and (B) of the upshifted-idler + original signal
biphotons. Theg(2)(t) peaks sit on a pedestal of accidental coincidences. The
ratio of bothg(2)(t) peaks is ~0.99 and the difference of their widths is
~25 ps, well below the minimum time step of ~50 ps resolvable with our
set-up. (C) Close-up of both measurements. The correlation peaks are
noncoincident in time owing to group-velocity dispersion in the fibers
delivering the single photons to the SSPDs.(^00) 0.1 0.2 0.3 0.4 0.5 0.6
20
40
60
80
100
Normalized photon numbers
Distance (m)
Stokes
Anti-Stokes
Biphoton idler Total
0.3 0.4 0.5 0.6
10 –4
10 –2
100
0 284 6 10 102
(x10–3)
–4 0 0.1 0.2 0.3 0.4 0.5 0.6
–2
0
2
4
Relative time (ns)
Distance (m)
4
2
0
–2
–4
4
2
0
–2
–4
0 0.1 0.2 0.3 0.4 0.5 0.6
Relative time (ns)
Distance (m)
0
Biphoton idler
Anti-Stokes
3 10x –4
01
Stokes
Biphoton idler
Coherence amplitude
ABC
Fig. 3. Numerical modeling of the frequency shifting process at 70 bar.
(A) Spatiotemporal evolution of Raman coherence inside the fiber. Time is
measured relative to a reference frame moving at the group velocity of the pump
pulses. (B) Evolution of the photon numbers normalized so that the efficiency
hcan be directly extracted. The signals displayed are the original idler (black solid
line), its Stokes (red solid line) and anti-Stokes (blue-dashed line) bands, and
their total sum (green-dotted line). The inset shows the detailed evolution over
the last 30 cm of fiber length (logarithmic vertical scale). (C) Spatiotemporal
evolution of the Stokes and anti-Stokes idler bands, normalized to the peak of the
anti-Stokes. The Stokes signal peaks after 30 cm and weakens as it propagates
further, owing to strong dephasing. In sharp contrast, the anti-Stokes light is
continuously amplified up to the fiber end face.
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