ARTICLE
On-chip coherent microwave-to-optical
transduction mediated by ytterbium in YVO
4
John G. Bartholomew
1,2,3,4,5
, Jake Rochman
1,2,3
, Tian Xie
1,2,3
, Jonathan M. Kindem
1,2,3,6,7,8
,
Andrei Ruskuc
1,2,3
, Ioana Craiciu
1,2,3
, Mi Lei
1,2,3
& Andrei Faraon
1,2,3
✉
Optical networks that distribute entanglement among various quantum systems will form a
powerful framework for quantum science but are yet to interface with leading quantum
hardware such as superconducting qubits. Consequently, these systems remain isolated
because microwave links at room temperature are noisy and lossy. Building long distance
connectivity requires interfaces that map quantum information between microwave and
optical
fi
elds. While preliminary microwave-to-optical transducers have been realized,
developing ef
fi
cient, low-noise devices that match superconducting qubit frequencies
(gigahertz) and bandwidths (10 kilohertz
–
1 megahertz) remains a challenge. Here we
demonstrate a proof-of-concept on-chip transducer using trivalent ytterbium-171 ions in
yttrium orthovanadate coupled to a nanophotonic waveguide and a microwave transmission
line. The device
′
s miniaturization, material, and zero-magnetic-
fi
eld operation are important
advances for rare-earth ion magneto-optical devices. Further integration with high quality
factor microwave and optical resonators will enable ef
fi
cient transduction and create
opportunities toward multi-platform quantum networks.
https://doi.org/10.1038/s41467-020-16996-x
OPEN
1
Thomas J. Watson, Sr., Laboratory of Applied Physics, California Institute of Technology, Pasadena, CA 91125, USA.
2
Kavli Nanoscience Institute, California
Institute of Technology, Pasadena, CA 91125, USA.
3
Institute for Quantum Information and Matter, California Institute of Technology, Pasadena, CA 91125,
USA.
4
Present address: School of Physics, The University of Sydney, Sydney, NSW 2006, Australia.
5
Present address: University of Sydney Nano Institute,
University of Sydney, Sydney, NSW 2006, Australia.
6
Present address: JILA, University of Colorado and NIST, Boulder, CO, USA.
7
Present address:
Department of Physics, University of Colorado, Boulder, CO, USA.
8
Present address: National Institute of Standards and Technology (NIST), Boulder, CO,
USA.
✉
email:
faraon@caltech.edu
NATURE COMMUNICATIONS
| (2020) 11:3266 | https://doi.org/10.1038/s41467-020-16996-x | www.nature.com/naturecommunications
1
1234567890():,;
R
are-earth ion (REI) ensembles simultaneously coupled
to optical and microwave resonators have been proposed
for microwave-to-opti
cal (M2O) transducers
1
,
2
that
could achieve an ef
fi
ciency and bandwidth to challenge other
leading protocols
3
,
4
. A further advantage of the REI platform
compared to electro-optical
5
,
6
, electro-optomechanical
7
,
8
,piezo-
optomechanical
9
,
10
, and other magneto-optical
11
schemes is the
existing REI infrastructure for building complex quantum-optical
networks
12
including sources
13
–
15
and memories
16
–
18
for quantum
states of light. While REIs provide promise for future networks,
transducer demonstrations have been limited to macroscopic
devices
19
,
20
. These millimeter-scale transducers currently require
high optical pump powers that will be challenging to integrate with
cryogenic cooling systems and light-sensitive superconducting
circuits
19
. In contrast, on-chip REI technologies provide strong
optical mode con
fi
nement to reduce the required pump power by
several orders of magnitude, and miniaturization expedites inte-
gration of multiple devices for powerful control of photons at the
quantum level. To achieve further integration with super-
conducting qubit platforms, it is also highly bene
fi
cial to extend
REI schemes
1
,
2
to zero magnetic
fi
eld operation
21
. Toward this
end, trivalent ytterbium-171 (
171
Yb
3
+
) is appealing because it
exhibits the simplest spin-state structure with gigahertz-frequency
hyper
fi
ne transitions
22
,
23
.
We report a miniaturized magneto-optic modulator based on
171
Yb
3
+
-doped yttrium orthovanadate (YVO
4
) that allowed low-
ef
fi
ciency coherent M2O transduction at near-zero and zero
magnetic
fi
eld. The concept for the proof-of-principle device is
shown in Fig.
1
a
–
c. The REI crystal was cooled and simulta-
neously coupled to optical and microwave excitations. The
coherence generated on the spin transition from excitation at
frequency
f
M
(3.4 GHz) is mapped to an optical coherence at
frequency
f
t
(304,505 GHz) through an optical pump
fi
eld at
frequency
f
o
. We measured the transduced signal at
f
t
using
optical heterodyne detection with a strong local oscillator at
frequency (
f
o
—
280 MHz). The ef
fi
ciency of the transduction is
currently limited by the weak coupling between the ion transi-
tions and the optical and microwave modes in the device
′
s
broadband waveguides. Future devices will harness on-chip cav-
ities to increase the mode coupling to progress toward ef
fi
cient
transduction operating at a quantum level.
Results
171
Yb
3
+
:YVO
4
device concept and fabrication
. A 30 μm-long
nanophotonic waveguide was fabricated in one of the gaps
between the ground and signal lines of a gold microwave
coplanar waveguide (Fig.
1
d). A photonic crystal mirror fabri-
cated on one end of the waveguide allowed optical
fi
elds to be
launched and collected from a single 45° coupler on the opposite
end of the device. We used waveguides to enable operation over a
wide frequency range and to test multiple optical and microwave
transitions but using cavities rather than waveguides in future
devices will dramatically increase the ef
fi
ciency of the trans-
duction process
19
,
20
. The device was thermally contacted to a
dilution refrigerator with a base temperature of ~30 mK (see
Methods section, and Supplementary Note 1 for further details).
While the device thermalized to 40 ± 10 mK, the waveguide
temperature during continuous transduction was estimated to be
~1 K due to the heating of the optical pump (see Supplementary
Note 9 for details).
To achieve ef
fi
cient M2O transduction using REI-doped
crystals, it is critical to have an ensemble with low inhomogeneity
and cavity coupled optical and microwave transitions with
collective cooperativities greater than unity
1
. The properties of
171
Yb
3
+
:YVO
4
can satisfy both requirements
22
. Signi
fi
cantly, the
171
Yb
3
+
optical transition near 984.5 nm exhibits a narrow
inhomogeneous linewidth (
Γ
ih,o
≈
200 MHz at a doping concen-
tration of ~100 ppm), and a large 4
f
–
4
f
oscillator strength (
f
=
5.3 × 10
−
6
), resulting in a magneto-optic nonlinear coef
fi
cient
100× larger than other REI-doped crystals considered for
transduction (see Supplementary Table 1 for details and
MW
a
bc
d
c
a
a
Refrigerator
External dc field coils
MW coil
B
ac
B
ac
| |
B
| |
c
B
f
M
f
ME
f
M
f
MG
f
t
f
t
f
o
f
o
f
o
f
t
PD
V system
Λ
system
|
e
2
〉
|
e
2
〉
|
e
1
〉
|
e
1
〉
|
g
2
〉
|
g
2
〉
|
g
1
〉
|
g
1
〉
Laser
+280 MHz
Fig. 1 Concept and miniaturized implementation of a rare-earth ion magneto-optic modulator. a
Conceptual schematic of the REI magneto-optic
modulator. A microwave
fi
eld
B
ac
is transduced to an optical
fi
eld (dotted coral line) using a REI ensemble in a crystal. The crystal is coupled to a
microwave transmission line (MW coil) and pumped by a laser
fi
eld (solid coral line). Magnetic
fi
eld coils provide control of the external dc
fi
eld
B
. The
transduced signal is combined with a frequency-shifted local oscillator on a photodiode to provide high signal-to-noise ratio heterodyne detectio
n.
b
Example three-level energy structures proposed for REI magneto-optic transducers with the input microwave (
f
M
), optical pump (
f
o
), and transduced
optical output (
f
t
).
c
Example four-level energy structure for transduction in zero magnetic
fi
eld with an additional microwave pump (
f
MG
).
d
False color
scanning electron microscope image of the planar, on-chip realization of the device in panel
a
(length of scale bar is equivalent to 10
μ
m). The 30
μ
m-long
waveguide had a single photonic crystal mirror de
fi
ned for the transverse magnetic mode (see inset: length of scale bar is equivalent to 4
μ
m). Light was
coupled to and collected from the device using the coupler formed from a 45° cut at one end of the waveguide (indicated by coral lines). The gold coplanar
waveguide provided a microwave frequency oscillating magnetic
fi
eld aligned with the crystal
c
-axis, while a home-built superconducting solenoid (not
shown) provided an external dc
fi
eld, also aligned with the crystal
c
-axis.
ARTICLE
NATURE COMMUNICATIONS | https://doi.org/10.1038/s41467-020-16996-x
2
NATURE COMMUNICATIONS
| (2020) 11:3266 | https://doi.org/10.1038/s41467-020-16996-x | www.nature.com/naturecommunications
Supplementary Note 2 for an overview of
171
Yb
3
+
:YVO
4
energy
levels).
171
Yb
3
+
ion optical properties and transduction strategies
.
Figure
2
a illustrates the zero-
fi
eld energy levels of
171
Yb
3
+
in
YVO
4
. For light polarized parallel to the crystal
c
-axis, only the
spin preserving transitions (A, E, and I) are allowed. The rela-
tively large hyper
fi
ne interaction means that the three optical
transitions are easily resolved in a waveguide transmission spec-
trum at zero magnetic
fi
eld (Fig.
2
b). Figure
2
highlights that
there are no V- or
Λ
-systems available for transduction with
magnetic
fi
eld magnitude |
B
|
=
0 for this polarization (the
statement also holds true for the orthogonal polarization, as
demonstrated in Supplementary Notes 7 and 8). We pursued two
strategies to mediate transduction. First, we created suitable
three-level systems by applying small magnetic
fi
elds along the
c
-
axis, which introduced spin-state mixing through the linear
Zeeman interaction. Second, we demonstrated a four-level
scheme that overcomes the need for applied magnetic
fi
elds. In
both cases we transduced microwave photons coupled to the spin
transition in the optical-excited state, which will allow future
transducers to bene
fi
t from decreased parasitic loss and dephas-
ing due to coupling with spectator-ion ensembles
24
.
Figure
2
c shows the normalized optical absorption of the ions
in the waveguide as a function of magnetic
fi
eld compared to the
predictions of the
171
Yb
3
+
spin Hamiltonian model
22
. Transi-
tions B and D become allowed for non-zero magnetic
fi
elds,
which can be used to form two V-systems and two
Λ
-systems. We
transduced classical microwave signals using the V-systems
containing the |1
〉
e
↔
|2
〉
e
transition:
f
M
=
3.369 GHz at |
B
|
≈
0
(Fig.
2
a).
M2O transduction using the V-system in a non-zero magnetic
fi
eld
. Figure
3
a shows example M2O transduction signals using
the three-level strategy as a function of laser excitation frequency
for increasing magnetic
fi
eld. When |
B
|
≠
0 and the ions are
optically driven on transition A (B) at an offset frequency
Δ
optical
around 0 GHz (0.675 GHz), microwave tones resonant with the
excited state transition are transduced to optical photons emitted
on the D (E) transition. Without cavity enhancement the trans-
duction signal is strongest for input
fi
elds resonant with the ion
transitions, whereas cavity coupling would allow high ef
fi
ciency
off resonance
1
,
25
. As the magnetic
fi
eld increases, the transduced
signal magnitude varies as the dipole moments and inhomo-
geneity of the optical and spin transitions change. Figure
3
b
shows a double resonance scan showing the transduced signal
intensity as a function of the pump frequency and the applied
microwave frequency for |
B
|
=
5.1 mT (see Supplementary
Notes 7 and 8 for additional data).
The high signal-to-noise ratio data was enabled by the optical
heterodyne detection, which overcomes the low device photon-
number ef
fi
ciency
η
=
1.2 × 10
−
13
(see Supplementary Note 3).
Given the characterization of our material, temperature, and
driving rates we expect to increase the device ef
fi
ciency by a factor
≥
3×10
12
by targeting optimized microwave and optical cavity
coupling (see Supplementary Note 4), and applying the optical
pump within the same cavity mode resonant with the signal. That
is, the same ensemble of
171
Yb
3
+
ions coupled to one-sided
microwave and optical resonators, each with a quality factor of
2×10
4
, could perform at an overall
η
> 0.3 with improvements to
the optical coupling ef
fi
ciency into a single mode
fi
ber (see
Supplementary Note 4). The dramatic increase in ef
fi
ciency is
possible because
η
scales quadratically with the photon
–
ion
coupling strength for
η
≪
1
19
,
20
.
To characterize the transducer
′
s bandwidth, we performed
pulsed M2O transduction measurements (shown in Fig.
3
c). The
decrease in signal for pulse lengths <10 μs suggests a bandwidth
limited by the spin transition inhomogeneity
Γ
ih
;
s
100 kHz,
which was con
fi
rmed by ensemble Rabi
fl
opping measurements
(
Γ
ih
;
s
¼
130 kHz
—
Supplementary Note 5). The current band-
width is similar to leading electro-optomechanical
8
transducers
but lower than the megahertz-bandwidths demonstrated in other
schemes
4
including REI demonstrations
19
,
20
. The bandwidth
could be increased by intentionally broadening
Γ
ih
;
s
through
increased dopant concentration or strain.
Performing transduction in atomic systems enables quantum
memories to be incorporated directly into the transduction
1
0.8
A
B
=0
a
b
c
Increasing
B
| |
c
AE I B D
0.746 GHz
3.369 GHz
0.674 GHz
2.073 GHz
2
F
5/2
(0)
2
F
7/2
(0)
E
Theory
1
0.6
0.8
0.4
0.2
0
Experiment
B
D
I
0.6
0.4
Transmission (norm.)
Magnetic field (mT)
Magnetic field (mT)
0.2
0
200
100
0
–100
–200
200
Transition
strength
100
0
–100
–200
–2
0
0
5
10
0
5
10
24
Δ
optical
(GHz)
Δ
optical
(GHz)
Δ
optical
(GHz)
6
8
10
12
|3
〉
e
,
|4
〉
e
|1
〉
g
,
|2
〉
g
|2
〉
e
|1
〉
e
|4
〉
g
|3
〉
g
Fig. 2 Magnetic
fi
eld dependence of
171
Yb
3
+
:YVO
4
optical transition
frequencies and strengths. a
Energy level structure for
171
Yb
3
+
:YVO
4
with
the permitted optical transitions for light polarized along the
c-
axis.
Transitions A (304,501.0 GHz
≈
984.54 nm), E, and I are the allowed, spin-
preserving transitions at zero magnetic
fi
eld, whereas transitions B and D
only become allowed for |
B
|
≠
0.
b
Transmission spectrum of the Yb
3
+
:
YVO
4
nanophotonic waveguide (total length
≈
60
μ
m) at a temperature of
~1 K at |
B
|
=
0. The light is polarized along the
c
-axis and the spectrum is
normalized to the transmission far off-resonance. The
171
Yb
3
+
transitions
(A, E, and I) are shaded blue and the impurity
even
Yb
3
+
transition is shaded
orange.
c
Comparison of the magnetic
fi
eld-dependent relative transition
strengths of ions in the waveguide device compared to the predicted
transition strengths from spin Hamiltonian theory
22
. Each horizontal slice of
the two-dimensional Experiment data is a normalized transmission
spectrum like that in
b
. The level of absorption is proportional to the
transition strength.
NATURE COMMUNICATIONS | https://doi.org/10.1038/s41467-020-16996-x
ARTICLE
NATURE COMMUNICATIONS
| (2020) 11:3266 | https://doi.org/10.1038/s41467-020-16996-x | www.nature.com/naturecommunications
3
protocol
2
to enable synchronization of network links. The
coherence lifetime of the spin transition
T
2 (Spin)
sets an upper
bound on the potential storage time. Using two-pulse Hahn
echoes we measure
T
2 (Spin)
=
35 μs as |
B
|
→
0 (see Supplemen-
tary Note 5), which is suf
fi
ciently long to enable useful storage
relative to the timescales of typical microwave qubit operations
(10
–
100 ns).
M2O transduction using a four-level system for |B|
=
0
. Using a
coherent three-level atomic system is a conceptually simple route
toward transduction between the microwave and optical domains.
There are, however, disadvantages to this scheme. Given a
fi
xed
pump
fi
eld, the strength of the optical photon
–
ion coupling is
reduced by at least a factor of 4 when using a V-system or
Λ
-
system. This is because the total oscillator strength of the optical
transition must be divided between the two optical branches.
Also, operating with a small bias magnetic
fi
eld is not ideal as it
will require shielding for integration with superconducting qubits.
We present an alternate transduction strategy using a four-level
system driven by an optical and a microwave pump as shown in
Fig.
4
a. The ideal implementation of this method harnesses the
full optical oscillator strength of the ions and for
171
Yb
3
+
:YVO
4
the four-level scheme enables transduction at zero magnetic
fi
eld.
The tradeoff for moving to the four-level scheme is the need for
an additional microwave drive tone resulting in more stringent
device criteria to operate at high ef
fi
ciency (see Supplementary
Note 6).
Figure
4
b shows a double resonance spectrum for the two
microwave inputs, with the optical pump
fi
eld
fi
xed at the
frequency of maximum transduction (
Δ
optical
=
0). In our
waveguide device the four-level scheme is less ef
fi
cient than the
three-level scheme and thus, requires increased laser power to
measure the signal. The resultant increase in device temperature
broadens the spin inhomogeneous linewidth, which in turn
decreases the ef
fi
ciency further. The signal modulation near
resonance for both microwave
fi
elds is most likely produced by
coherent destructive interference at speci
fi
c population differ-
ences between the four levels
25
.
Discussion
This waveguide device illustrates the appeal of miniaturized REI
devices for quantum photonic applications. We have demon-
strated coherent M2O transduction, presented a strategy to
improve the ef
fi
ciency to >30%, and extended the protocol to
zero-magnetic-
fi
eld operation. The enabling high spectral density
of the
171
Yb
3
+
transitions can also be applied to realize other
quantum photonic interfaces such as sources and memories (see
Supplementary Note 10 for preliminary optical measurements).
Future work will target highly ef
fi
cient transducers that will allow
a detailed noise analysis of the protocol, and ultimately their
integration with photonic quantum memories
23
and
171
Yb
3
+
-ion
single photon sources
15
to create the interfaces for hybrid
quantum networks.
Methods
Device
. A 5 nm-thick layer of chromium and a 115 nm-thick layer of gold was
depositedona3×3×0.5mm(
a
×
a
×
c
)86ppm
171
Yb
3
+
-doped YVO
4
crystal
15.93, 3.415
3.4
a
bc
D
EB
A
6
4
2
0
01
–0.5
0
0.5
0
51015
1
3.39
dBm
–75
–80
–85
–90
–95
–100
–105
3.38
3.37
|
B
|
(mT),
f
M
(GHz)
|
B
|
= 5.10 mT
f
M
(GHz)
Δ
optical
(GHz)
Δ
optical
(GHz)
Δ
optical
=
0 GHz
Δ
optical
=
0.675 GHz
Time (
μ
s)
22.7 dB
Transduced signal (dB)
Transduced signal (norm.)
14.38, 3.407
12.84, 3.399
11.29, 3.392
9.74, 3.386
8.20, 3.381
6.65, 3.377
5.10, 3.374
3.56, 3.371
2.01, 3.369
0.46, 3.369
Fig. 3 Continuous wave and pulsed microwave-to-optical transduction from the waveguide device. a
Transduction signal produced at the D and E optical
transition frequencies as a function of the applied
fi
eld along the
c
-axis. The transduction is mediated by optically driving transitions A (
Δ
optical
=
0 GHz)
and B (
Δ
optical
=
0.675 GHz) in their respective V-systems. The signal is optimized when the input microwave
fi
eld frequency
f
M
is resonant with the
excited state hyper
fi
ne transition at ~3.4 GHz.
b
A double resonance scan showing the transduced signal as a function of both the optical and microwave
frequencies, which provides an indication of the inhomogeneous broadening of the relevant transitions. (Detection bandwidth
=
3 kHz, optical pump power
in the waveguide
=
2
μ
W, Rabi frequency
Ω
o
≈
6 MHz, and microwave power of
−
5.3 dBm in the coplanar waveguide, Rabi frequency
Ω
m
≈
1 MHz.) White
curves show the transduced signal (log scale) as a function of
f
M
at the middle of the optical inhomogeneous line.
c
Pulsed transduction signals (offset for
clarity) generated at
f
t
(blue) at the maximum ef
fi
ciency point in
b
. The yellow pulse indicates excitation at
f
o
only, whereas during the purple pulses the
ensemble is excited with both
f
o
and
f
M
generating the transduced
fi
eld.
2
F
7/2
(0)
f
MG
(GHz)
f
ME
(GHz)
AE
B
= 0
2
F
5/2
(0)
0.72
0.7
0.68
0.66
0.64
3.32 3.34 3.36 3.38
3.4
3.42
–105
dBm
a
b
–110
–115
–120
–125
f
ME
f
MG
|2
〉
e
|1
〉
e
|4
〉
g
|3
〉
g
Fig. 4 Four-level system transduction at zero
fi
eld. a
The energy levels
used for a four-level magneto-optical transduction scheme at zero magnetic
fi
eld using
171
Yb
3
+
:YVO
4
. The input microwave
fi
eld at the excited state
hyper
fi
ne transition frequency
f
ME
is transduced to an output optical
fi
eld
resonant with transition E. The ions are pumped by a microwave
fi
eld
resonant with the ground state hyper
fi
ne transition
f
MG
and an optical
fi
eld
resonant with transition A.
b
Transduced signal at the frequency of the
optical transition E as a function of the two microwave input signals with
the detuning of the optical pump
Δ
optical
=
0, which provides an indication
of the inhomogeneous broadening of the relevant transitions (detection
bandwidth
=
30 Hz, optical pump power in the waveguide
=
25
μ
W, Rabi
frequency
Ω
o
≈
20 MHz, and microwave power of 3.7 dBm in the coplanar
waveguide, Rabi frequency
Ω
ME
≈
3 MHz,
Ω
MG
≈
10 MHz).
ARTICLE
NATURE COMMUNICATIONS | https://doi.org/10.1038/s41467-020-16996-x
4
NATURE COMMUNICATIONS
| (2020) 11:3266 | https://doi.org/10.1038/s41467-020-16996-x | www.nature.com/naturecommunications
(Gamdan Optics) using electron beam evaporation (CHA Industries Mark 40). A
coplanar waveguide was fabricated from the gold layer using electron beam
lithography (Raith EBPG 5000
+
) followed by wet-etching in gold etchant.
The photonic structures were milled within the coplanar waveguide gaps using
aGa
+
focused ion beam (FEI Nova 600 Nanolab). The underlying structure for the
nanophotonic waveguide is a suspended beam with an equilateral triangular cross
section with each side equal to ~1 μm. A distributed Bragg re
fl
ecting mirror was
then milled into the waveguide, using similar cuts used to de
fi
ne photonic crystal
resonators in our previous work
26
.
Experimental setup
. The device chip was bonded to an oxygen-free high thermal
conductivity (OFHC) copper sample holder using a thin layer of silver paint
(Pelco). The gold coplanar waveguide was wire bonded to a PCB board from
Montana Instruments
fi
tted with SMP-type coaxial connectors. The sample
holder was incorporated into a home-built, OFHC copper apparatus attached to
the mixing chamber of a BlueFors dilution refrigerator. The apparatus incor-
porates a homebuilt superconducting solenoid (
fi
eld coef
fi
cient
=
77.3 mT/A)
and a
fi
ber-coupled-lens pair mounted onto a three-axis nanopositioner
(Attocube).
Continuous-wave transduction measurements were made using a Field Fox
N9115A spectrum analyzer. Optical signals from the device were combined with a
strong optical local oscillator on a 50:50
fi
ber beam splitter. The output from the
beam splitter was detected by an InGaAs
fi
ber-coupled photodetector with a 5 GHz
bandwidth (Thorlabs DET08CFC). The output from the detector was
fi
ltered using
a bias-tee (Minicircuits ZFBT4B2GW
+
) and the strong beat signal at the local
oscillator offset frequency (280 MHz) was suppressed using a band-block
fi
lter (RF
Bay BSF-280M). The signal was then ampli
fi
ed (Pasternack PE15A1010) before
being detected by the Field Fox receiver.
For the time domain measurements, the ampli
fi
ed signal was further ampli
fi
ed
by two Minicircuits ZX60-3800LN-S
+
ampli
fi
ers and mixed down (Minicircuits
ZX05-30W-S
+
) to a frequency of 21.4 MHz using a local oscillator signal at
~3.6704 GHz (TPI-1002-A). The lower frequency signal was then
fi
ltered
(Minicircuits BBP-21.4), ampli
fi
ed (SR445), and detected on a TDS7104
oscilloscope. To gate the microwave input to the device we used a Minicircuits
ZASWA-2-50DR
+
TTL-controlled switch.
The optical excitation was provided by a cw titanium sapphire laser (either M
2
SolsTiS or Coherent MBR). For higher precision measurements, the SolsTiS was
locked to an ultra-low expansion reference cavity (Stable Laser systems) with a
controllable offset frequency provided by an electro-optic modulator (IX Blue). The
laser light was
fi
ber coupled and sent through a free space polarization controller.
The polarized light was then split into two paths, one acting as the sample pump
beam, and the other as the optical local oscillator. The pump beam was frequency
shifted and gated through a
fi
ber acousto-optic modulator (AOM
—
Brimrose) and
input into the fridge using a circulator.
Absorption measurements were performed using a home-built external cavity
diode laser. In this case, the transmitted light was detected by a switchable gain
InGaAs photodetector (Thorlabs PDA10) or a Perkin Elmer APD. In the case of
photon counting experiments, time tagging was performed by Sensl or Picoquant
data acquisition electronics.
For pulsed all-optical measurements, the input light was gated using two
double-pass AOMs (Intraction) and the signal gated by a third single-pass AOM
before detection on the APD.
For further details refer to Supplementary Note 1 and Supplementary Fig. 1.
Data availability
The data that support the
fi
ndings of this study are available from the corresponding
author upon reasonable request.
Received: 2 April 2020; Accepted: 5 June 2020;
References
1. Williamson, L. A., Chen, Y.-H. & Longdell, J. J. Magneto-optic modulator with
unit quantum ef
fi
ciency.
Phys. Rev. Lett.
113
,1
–
5 (2014).
2. O
’
Brien, C., Lauk, N., Blum, S., Morigi, G. & Fleischhauer, M. Interfacing
superconducting qubits and telecom photons via a rare-earth-doped crystal.
Phys. Rev. Lett.
113
,1
–
5 (2014).
3. Lambert, N. J., Rueda, A., Sedlmeir, F. & Schwefel, H. G. L. Coherent
conversion between microwave and optical photons
—
an overview of physical
implementations.
Adv. Quantum Technol.
3
, 1900077 (2020).
4. Lauk, N. et al. Perspectives on quantum transduction.
Quantum Sci. Technol.
5
, 020501 (2020).
5. Rueda, A. et al. Ef
fi
cient microwave to optical photon conversion: an electro-
optical realization.
Optica
3
, 597 (2016).
6. Fan, L. et al. Superconducting cavity electro-optics: a platform for coherent
photon conversion between superconducting and photonic circuits.
Sci. Adv.
4
, eaar4994 (2018).
7. Andrews, R. W. et al. Bidirectional and ef
fi
cient conversion between
microwave and optical light.
Nat. Phys.
10
, 321
–
326 (2014).
8. Higginbotham, A. P. et al. Harnessing electro-optic correlations in an ef
fi
cient
mechanical converter.
Nat. Phys.
14
, 1038
–
1042 (2018).
9. Vainsencher, A., Satzinger, K. J., Peairs, G. A. & Cleland, A. N. Bi-directional
conversion between microwave and optical frequencies in a piezoelectric
optomechanical device.
Appl. Phys. Lett.
109
, 033107 (2016).
10. Dahmani, Y. D., Sarabalis, C. J., Jiang, W., Mayor, F. M. & Safavi-Naeini, A. H.
Piezoelectric transduction of a wavelength-scale mechanical waveguide.
Phys.
Rev. Appl.
13
, 024069 (2020).
11. Hisatomi, R. et al. Bidirectional conversion between microwave and light via
ferromagnetic magnons.
Phys. Rev. B
93
, 174427 (2016).
12. Wehner, S., Elkouss, D. & Hanson, R. Quantum internet: a vision for the road
ahead.
Science
362
, eaam9288 (2018).
13. Ledingham, P. M., Naylor, W. R. & Longdell, J. J. Experimental realization of
light with time-separated correlations by rephasing ampli
fi
ed spontaneous
emission.
Phys. Rev. Lett.
109
, 093602 (2012).
14. Dibos, A. M., Raha, M., Phenicie, C. M. & Thompson, J. D. Atomic source of
single photons in the telecom band.
Phys. Rev. Lett.
120
, 243601 (2018).
15. Kindem, J. M. et al. Control and single-shot readout of an ion embedded in a
nanophotonic cavity.
Nature
580
, 201
–
204 (2020).
16. Hedges, M. P., Longdell, J. J., Li, Y. & Sellars, M. J. Ef
fi
cient quantum memory
for light.
Nature
465
, 1052
–
1056 (2010).
17. Gündo
ğ
an, M., Ledingha, P.M., Kutluer, K., Mazzera, M. & de Riedma, H.
Solid state spin-wave quantum memory for time-bin qubits.
Phys. Rev. Lett.
114
, 230501 (2015).
18. Jobez, P. et al. Coherent spin control at the quantum level in an ensemble-
based optical memory.
Phys. Rev. Lett.
114
, 230502 (2015).
19. Fernandez-Gonzalvo, X., Chen, Y.-H., Yin, C., Rogge, S. & Longdell, J. J.
Coherent frequency up-conversion of microwaves to the optical
telecommunications band in an Er:YSO crystal.
Phys. Rev. A
92
, 062313 (2015).
20. Fernandez-Gonzalvo, X., Horvath, S. P., Chen, Y.-H. & Longdell, J. J. Cavity-
enhanced Raman heterodyne spectroscopy in Er
3
+
:Y
2
SiO
5
.
Phys. Rev. A
100
,
033807 (2019).
21. Chen, Y.-H., Fernandez-Gonzalvo, X. & Longdell, J. J. Coupling erbium spins
to a three-dimensional superconducting cavity at zero magnetic
fi
eld.
Phys.
Rev. B
94
,1
–
5 (2016).
22. Kindem, J. M. et al. Characterization of
171
Yb
3
+
:YVO
4
for photonic quantum
technologies.
Phys. Rev. B
98
, 024404 (2018).
23. Ortu, A. et al. Simultaneous coherence enhancement of optical and microwave
transitions in solid-state electronic spins.
Nat. Mater.
17
, 671
–
675 (2018).
24. Welinski, S. et al. Electron spin coherences in rare-earth optically excited
states for microwave to optical quantum transducers.
Phys. Rev. Lett.
122
,
247401 (2018).
25. Fernandez-Gonzalvo, X. Coherent frequency conversion from microwave to
optical
fi
elds in an erbium doped Y
2
SiO
5
crystal: towards the single photon
regime. PhD thesis, University of Otago (2017).
26. Zhong, T., Rochman, J., Kindem, J. M., Miyazono, E. & Faraon, A. High
quality factor nanophotonic resonators in bulk rare-earth doped crystals.
Opt.
Express
24
, 536 (2016).
Acknowledgements
This work was funded by Of
fi
ce of Naval Research Young Investigator Award No. N00014-
16-1-2676, Of
fi
ce of Naval Research Award No. N00014-19-1-2182, Air Force Of
fi
ce of
Scienti
fi
c Research grant number FA9550-18-1-0374, Army Research Of
fi
ce (ARO/LPS)
(CQTS) grant number W911NF1810011, Northrop Grumman and Weston Havens
Foundation. The device nanofabrication was performed in the Kavli Nanoscience Institute
at the California Institute of Technology. J.G.B. acknowledges the support of the American
Australian Association
′
s Northrop Grumman Fellowship. I.C. and J.R. acknowledge support
from the Natural Sciences and Engineering Research Council of Canada (Grant Nos.
PGSD2-502755-2017 and PGSD3-502844-2017). The authors would like to acknowledge
Jevon Longdell, Yu-Hui Chen, Tian Zhong, and Mike Fitelson for useful discussions.
Author contributions
J.G.B., J.R., T.X., and A.F. designed the experiments. J.G.B., J.R., T.X., J.M.K., A.R., I.C.,
M.L., contributed to the construction of the experimental apparatus. J.R. fabricated the
device, and J.G.B. and T.X. performed the experiments, with support from all other
authors. J.G.B., J.R., and T.X. conducted the data analysis and modeling. J.G.B. and A.F.
wrote the manuscript with input from all authors.
Competing interests
The authors declare no competing interests.
NATURE COMMUNICATIONS | https://doi.org/10.1038/s41467-020-16996-x
ARTICLE
NATURE COMMUNICATIONS
| (2020) 11:3266 | https://doi.org/10.1038/s41467-020-16996-x | www.nature.com/naturecommunications
5
Additional information
Supplementary information
is available for this paper at
https://doi.org/10.1038/s41467-
020-16996-x
.
Correspondence
and requests for materials should be addressed to A.F.
Peer review information
Nature Communications
thanks the anonymous reviewer(s) for
their contribution to the peer review of this work.
Reprints and permission information
is available at
http://www.nature.com/reprints
Publisher
’
s note
Springer Nature remains neutral with regard to jurisdictional claims in
published maps and institutional af
fi
liations.
Open Access
This article is licensed under a Creative Commons
Attribution 4.0 International License, which permits use, sharing,
adaptation, distribution and reproduction in any medium or format, as long as you give
appropriate credit to the original author(s) and the source, provide a link to the Creative
Commons license, and indicate if changes were made. The images or other third party
material in this article are included in the article
’
s Creative Commons license, unless
indicated otherwise in a credit line to the material. If material is not included in the
article
’
s Creative Commons license and your intended use is not permitted by statutory
regulation or exceeds the permitted use, you will need to obtain permission directly from
the copyright holder. To view a copy of this license, visit
http://creativecommons.org/
licenses/by/4.0/
.
© The Author(s) 2020
ARTICLE
NATURE COMMUNICATIONS | https://doi.org/10.1038/s41467-020-16996-x
6
NATURE COMMUNICATIONS
| (2020) 11:3266 | https://doi.org/10.1038/s41467-020-16996-x | www.nature.com/naturecommunications