A Ku band pulsed electron paramagnetic resonance spectrometer using an arbitrary waveform generator for quantum control experiments at millikelvin temperatures

Abstract

We present a 17 GHz (Ku band) arbitrary waveform pulsed electron paramagnetic resonance spectrometer for experiments down to millikelvin temperatures. The spectrometer is located at room temperature, while the resonator is placed either in a room temperature magnet or inside a cryogen-free dilution refrigerator; the operating temperature range of the dilution unit is from ca. 10 mK to 8 K. This combination provides the opportunity to perform quantum control experiments on electron spins in the pure-state regime. At 0.6 T, spin echo experiments were carried out using γ-irradiated quartz glass from 1 K to 12.3 mK. With decreasing temperatures, we observed an increase in spin echo signal intensities due to increasing spin polarizations, in accordance with theoretical predictions. Through experimental data fitting, thermal spin polarization at 100 mK was estimated to be at least 99%, which was almost pure state. Next, to demonstrate the ability to create arbitrary waveform pulses, we generate a shaped pulse by superposing three Gaussian pulses of different frequencies. The resulting pulse was able to selectively and coherently excite three different spin packets simultaneously-a useful ability for analyzing multi-spin system and for controlling a multi-qubit quantum computer. By applying this pulse to the inhomogeneously broadened sample, we obtain three well-resolved excitations at 8 K, 1 K, and 14 mK.

Storage and retrieval of microwave pulses with molecular spin ensembles

“…At this point the excitations are retrieved as an echo train. In other words, the ensemble has kept trace of the initial excitations 9,47,48,60 .…”

Room temperature hyperpolarization of polycrystalline samples with optically polarized triplet electrons: Pentacene or Nitrogen-Vacancy center in diamond?

“…The EPR experiments were done with a home-built spectrometer, similar to Ref. (Yap et al, 2015), where an RF pulse at 400 MHz generated by arbitrary waveform generator was converted to 11.6 GHz in a superheterodyne architecture. The microwave pulse was amplified to 1 W and led into the cavity.…”

Room-temperature hyperpolarization of polycrystalline samples with optically polarized triplet electrons: pentacene or nitrogen-vacancy center in diamond?

“…7c). We estimated the active spin-packet fraction η PBA p and the triplet fraction η P t of pentacene in a similar way to the case The average electron polarization P P e between the two triplet sublevels over the field-sweep time was estimated using the populations over the zero-field eigenstates of the triplet state of pentacene doped in benzoic acid, which is known to be P x : P y : P z = 0.44 : 0.34 : 0.22 (Yu et al, 1984). Assuming that the external magnetic field is nearly perpendicular to the z axis of the principal axis system of the ZFS tensor for the relevant electron-spin packets, we calculated the populations over the triplet sublevels in the magnetic field and obtained P P e = 0.105 and η P t = 2/(3 − P P e ) = 0.69.…”

“…For the NV − centers, the ground state is the triplet state, while in the case of pentacene, the ground state is the singlet state (S = 0). The zerofield splitting (ZFS) parameters D and E are 2870 MHz and ∼ 0 MHz for the NV − center and ∼ 1350 and ∼ 42 MHz for pentacene in the excited state, the latter of which may vary depending on the host molecule (Yu et al, 1984). The differences between these two systems are summarized in Table 1.…”

“…The x, y, and z axes represent the principal axes of the ZFS tensor. (c) Orientational dependence of the polarization of the electron spins in the photo-excited triplet state of pentacene doped in benzoic acid in 0.39 T calculated from the zero-field population(Yu et al, 1984). The upper and lower rows correspond to the EPR transitions between the m S = +1 and m S = 0 states and between the m S = 0 and m S = −1 states, respectively.…”