6 research outputs found
Normal-mode splitting in the coupled system of hybridized nuclear magnons and microwave photons
In the weak ferromagnetic MnCO system, a low-frequency collective spin
excitation (magnon) is the hybridized oscillation of nuclear and electron spins
coupled through the hyperfine interaction. By using a split-ring resonator, we
performed transmission spectroscopy measurements of MnCO system and
observed, for the first time, avoiding crossing between the hybridized
nuclear-electron magnon mode and the resonator mode in the NMR-frequency range.
The splitting strength is quite large due to the large spin density of
Mn, and the cooperativity value (magnon-photon coupling
parameter) is close to the conditions of strong coupling. The results reveal a
new class of spin systems, in which the coupling between nuclear spins and
photons is mediated by electron spins via the hyperfine interaction, and in
which the similar normal-mode splitting of the hybridized nuclear magnon mode
and the resonator mode can be observed.Comment: 5 pages, 3 figure
Identification of different types of high-frequency defects in superconducting qubits
Parasitic two-level-system (TLS) defects are one of the major factors
limiting the coherence times of superconducting qubits. Although there has been
significant progress in characterizing basic parameters of TLS defects, exact
mechanisms of interactions between a qubit and various types of TLS defects
remained largely unexplored due to the lack of experimental techniques able to
probe the form of qubit-defect couplings. Here we present an experimental
method of TLS defect spectroscopy using a strong qubit drive that allowed us to
distinguish between various types of qubit-defect interactions. By applying
this method to a capacitively shunted flux qubit, we detected a rare type of
TLS defects with a nonlinear qubit-defect coupling due to critical-current
fluctuations, as well as conventional TLS defects with a linear coupling to the
qubit caused by charge fluctuations. The presented approach could become the
routine method for high-frequency defect inspection and quality control in
superconducting qubit fabrication, providing essential feedback for fabrication
process optimization. The reported method is a powerful tool to uniquely
identify the type of noise fluctuations caused by TLS defects, enabling the
development of realistic noise models relevant to fault-tolerant quantum
control
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
Submicrometer-scale temperature sensing using quantum coherence of a superconducting qubit
Interest is growing in the development of quantum sensing based on the principles of quantum mechanics, such as discrete energy levels, quantum superposition, and quantum entanglement. Superconducting flux qubits are quantum two-level systems whose energy is sensitive to a magnetic field. Therefore, they can be used as high-sensitivity magnetic field sensors that detect the magnetization of a spin ensemble. Since the magnetization depends on temperature and the magnetic field, the temperature can be determined by measuring the magnetization using the flux qubit. In this study, we demonstrated highly sensitive temperature sensing with high spatial resolution as an application of a magnetic field sensor using the quantum coherence of a superconducting flux qubit. By using a superconducting flux qubit to detect the temperature dependence of the polarization ratio of electron spins in nano-diamond particles, we succeeded in measuring the temperature with a sensitivity of 1.3 µ Kµ at T  = 9.1 mK in the submicrometer range