Article
https://doi.org/10.1038/s41467-023-36799-0
Microwave-to-optical transduction with
erbium ions coupled to planar photonic
and superconducting resonators
Jake Rochman
1,2,5
, Tian Xie
1,2,5
, John G. Bartholomew
1,2,3,4
,K.C.Schwab
1,2
&
Andrei Faraon
1,2
Optical quantum networks
can connect distant quantum processors to enable
secure quantum communication and distributed quantum computing.
Superconducting qubits are a leading technology for quantum information
processing but cannot couple to long-
distance optical networks without an
ef
fi
cient, coherent, and low noise inte
rface between microwave and optical
photons. Here, we demonstrate a microwave-to-optical transducer using an
ensemble of erbium ions that is simultaneously coupled to a superconducting
microwave resonator and a nanophotonic optical resonator. The coherent
atomic transitions of the ions mediate the frequency conversion from micro-
wave photons to optical photons and us
ing photon counting we observed
device conversion ef
fi
ciency approaching 10
−
7
.Withpulsedoperationatalow
duty cycle, the device maintained a
spin temperature below 100 mK and
microwave resonator heating of less than 0.15 quanta.
Quantum transducers that convert p
hotons between different energies
are essential components of a hybrid quantum network
1
,
2
.Transducers
that operate between microwave and optical frequencies are of parti-
cular interest to interface state-of-the-art cryogenic superconducting
quantum circuits
3
, with excitations at microwave frequencies, and room
temperature optical quantum n
etworks using telecom photons
4
.Ef
fi
-
cient, low-noise, and high bandwidth microwave-to-optical quantum
transducers can permit superconducting circuits to function within
large-scale and long-distance quantum communication and distributed
quantum computing systems
5
,
6
.High-ef
fi
ciency transduction requires
strong coupling between the transduction medium and both optical
and microwave photons. Low noise
transduction requires low tem-
perature operation (T <
_
ω
/k
B
), and minimal decoherence or added
parasitic photons from the conversion process. Efforts to develop a
microwave-to-optical transducer have focused on schemes using an
intermediate mechanical mode
7
,
8
or electro-optic materials
9
,
10
, while
other approaches, such as atomic ensembles
11
–
13
or magnonic systems
14
,
have also been demonstrated recently.
Ensembles of rare-earth ions (REIs) in crystals offer a promising
platform for microwave-to-optical transduction (Fig.
1
a). Ef
fi
cient
transduction can be achieved by simultaneous strong ensemble cou-
pling of REI
’
s Zeeman or hyper
fi
ne transitions to a microwave reso-
nator and their coherent 4f-4f optical transitions to an optical cavity.
Also, REIs offer advantages for operating in the low noise regime due
to the absence of a mechanical mode that can be susceptible to ther-
mal excitations and they have narrow atomic transition inhomogene-
ities (i.e. much smaller than the microwave transduction frequency)
that intrinsically minimize the Stokes noise process
15
.Further,REIs
systems have demonstrated additional quantum network resources
such as quantum memories
16
and single-photon sources
17
,
18
, which can
enable additional functionality when combined with a REI-based
transducer.
Previous REI transducers include bulk crystals with macroscopic
resonators that require high optical pump power
11
or on-chip optical
and microwave waveguides with limited ef
fi
ciency
12
.Theseimple-
mentations have used a Raman scattering protocol that requires a
Received: 14 July 2022
Accepted: 17 February 2023
Check for updates
1
Kavli Nanoscience Institute and Thomas J. Watson, Sr., Laboratory of Applied Physics, California Institute of Technology, Pasadena, CA 91125, USA.
2
Institute
for Quantum Information and Matter, California Institute of Technology, Pasadena, CA 91125, USA.
3
The University of Sydney Nano Institute, The University of
Sydney, Sydney, NSW 2006, Australia.
4
Present address: Centre for Engineered Quantum Systems, School of Physics, The University of Sydney, Sydney, NSW
2006, Australia.
5
These authors contributed equally: Jake Rochman, Tian Xie.
e-mail:
faraon@caltech.edu
Nature Communications
| (2023) 14:1153
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