17 research outputs found
Quantitative modeling of superconducting planar resonators with improved field homogeneity for electron spin resonance
We present three designs for planar superconducting microwave resonators for
electron spin resonance (ESR) experiments. We implement finite element
simulations to calculate the resonance frequency and quality factors as well as
the three-dimensional microwave magnetic field distribution of the resonators.
One particular resonator design offers an increased homogeneity of the
microwave magnetic field while the other two show a better confinement of the
mode volume. We extend our model simulations to calculate the collective
coupling rate between a spin ensemble and a microwave resonator in the presence
of an inhomogeneous magnetic resonator field. Continuous-wave ESR experiments
of phosphorus donors in Si demonstrate the feasibility of our
resonators for magnetic resonance experiments. We extract the collective
coupling rate and find a good agreement with our simulation results,
corroborating our model approach. Finally, we discuss specific application
cases for the different resonator designs
Maser threshold characterization by resonator Q-factor tuning
Whereas the laser is nowadays an ubiquitous technology, applications for its microwave
analog, the maser, remain highly specialized, despite the excellent low-noise microwave
amplification properties. The widespread application of masers is typically limited by the need
of cryogenic temperatures. The recent realization of a continuous-wave room-temperature
maser, using NV− centers in diamond, is a first step towards establishing the maser as a
potential platform for microwave research and development, yet its design is far from optimal. Here, we design and construct an optimized setup able to characterize the operating
space of a maser using NV− centers. We focus on the interplay of two key parameters for
emission of microwave photons: the quality factor of the microwave resonator and the degree
of spin level-inversion. We characterize the performance of the maser as a function of these
two parameters, identifying the parameter space of operation and highlighting the requirements for maximal continuous microwave emission
Nonlinear magnon polaritons
We experimentally and theoretically demonstrate that nonlinear spin-wave
interactions suppress the hybrid magnon-photon quasiparticle or "magnon
polariton" in microwave spectra of an yttrium iron garnet film detected by an
on-chip split-ring resonator. We observe a strong coupling between the Kittel
and microwave cavity modes in terms of an avoided crossing as a function of
magnetic fields at low microwave input powers, but a complete closing of the
gap at high powers. The experimental results are well explained by a
theoretical model including the three-magnon decay of the Kittel magnon into
spin waves. The gap closure originates from the saturation of the ferromagnetic
resonance above the Suhl instability threshold by a coherent back reaction from
the spin waves.Comment: 6 page
Spin resonance linewidths of bismuth donors in silicon coupled to planar microresonators
Ensembles of bismuth donor spins in silicon are promising storage elements
for microwave quantum memories due to their long coherence times which exceed
seconds. Operating an efficient quantum memory requires achieving critical
coupling between the spin ensemble and a suitable high-quality factor resonator
-- this in turn requires a thorough understanding of the lineshapes for the
relevant spin resonance transitions, particularly considering the influence of
the resonator itself on line broadening. Here, we present pulsed electron spin
resonance measurements of ensembles of bismuth donors in natural silicon, above
which niobium superconducting resonators have been patterned. By studying spin
transitions across a range of frequencies and fields we identify distinct line
broadening mechanisms, and in particular those which can be suppressed by
operating at magnetic-field-insensitive `clock transitions'. Given the donor
concentrations and resonator used here, we measure a cooperativity
and based on our findings we discuss a route to achieve unit cooperativity, as
required for a quantum memory
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Strain in heterogeneous quantum devices with atomic layer deposition
Abstract: We investigated the use of dielectric layers produced by atomic layer deposition (ALD) as an approach to strain mitigation in composite silicon/superconductor devices operating at cryogenic temperatures. We show that the addition of an ALD layer acts to reduce the strain of spins closest to silicon/superconductor interface where strain is highest. We show that appropriately biasing our devices at the hyperfine clock transition of bismuth donors in silicon, we can remove strain broadening and that the addition of ALD layers left T 2 (or temporal inhomogeneities) unchanged in these natural silicon devices
Coherent spin dynamics of rare-earth doped crystals in the high-cooperativity regime
Rare-earth doped crystals have long coherence times and the potential to
provide quantum interfaces between microwave and optical photons. Such
applications benefit from a high cooperativity between the spin ensemble and a
microwave cavity -- this motivates an increase in the rare earth ion
concentration which in turn impacts the spin coherence lifetime. We measure
spin dynamics of two rare-earth spin species, Nd and Yb doped into
YSiO, coupled to a planar microwave resonator in the high
cooperativity regime, in the temperature range 1.2 K to 14 mK. We identify
relevant decoherence mechanisms including instantaneous diffusion arising from
resonant spins and temperature-dependent spectral diffusion from impurity
electron and nuclear spins in the environment. We explore two methods to
mitigate the effects of spectral diffusion in the Yb system in the
low-temperature limit, first, using magnetic fields of up to 1 T to suppress
impurity spin dynamics and, second, using transitions with low effective
g-factors to reduce sensitivity to such dynamics. Finally, we demonstrate how
the `clock transition' present in the Yb system at zero field can be
used to increase coherence times up to ms.Comment: 8 pages, 5 figure
Random-access quantum memory using chirped pulse phase encoding
Quantum memories capable of faithfully storing and recalling quantum states
on-demand are powerful ingredients in bulding quantum networks
[arXiv:0806.4195] and quantum information processors [arXiv:1109.3743]. As in
conventional computing, key attributes of such memories are high storage
density and, crucially, random access, or the ability to read from or write to
an arbitrarily chosen register. However, achieving such random access with
quantum memories [arXiv:1904.09643] in a dense, hardware-efficient manner
remains a challenge, for example requiring dedicated cavities per qubit
[arXiv:1109.3743] or pulsed field gradients [arXiv:0908.0101]. Here we
introduce a protocol using chirped pulses to encode qubits within an ensemble
of quantum two-level systems, offering both random access and naturally
supporting dynamical decoupling to enhance the memory lifetime. We demonstrate
the protocol in the microwave regime using donor spins in silicon coupled to a
superconducting cavity, storing up to four multi-photon microwave pulses and
retrieving them on-demand up to 2~ms later. A further advantage is the natural
suppression of superradiant echo emission, which we show is critical when
approaching unit cooperativity. This approach offers the potential for
microwave random access quantum memories with lifetimes exceeding seconds
[arXiv:1301.6567, arXiv:2005.09275], while the chirped pulse phase encoding
could also be applied in the optical regime to enhance quantum repeaters and
networks