Electron paramagnetic resonance spectroscopy using a direct current-SQUID magnetometer directly coupled to an electron spin ensemble

Toida, Hiraku; Matsuzaki, Yuichiro; Kakuyanagi, Kosuke; Zhu, Xiaobo; Munro, William J.; Nemoto, Kae; Yamaguchi, Hiroshi; Saito, Shiro

doi:10.1063/1.4940978

Cited by 31 publications

(36 citation statements)

References 22 publications

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“…Due to the ∼μm size of the SQUID and the fast decay of the microwave field, the effective detected sample volume is estimated as in Ref. [27] to be ∼μm 3 size, which corresponds to ∼ 10 7 spins in the case of the CaWO 4 :Gd 3+ sample discussed here.…”

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confidence: 99%

Sensitive spin detection using an on-chip SQUID-waveguide resonator

Yue

Chen

Barreda

et al. 2017

Applied Physics Letters

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Precise detection of spin resonance is of paramount importance to achieve coherent spin control in quantum computing. We present a novel setup for spin resonance measurements, which uses a dc-SQUID flux detector coupled to an antenna from a coplanar waveguide. The SQUID and the waveguide are fabricated from 20 nm Nb thin film, allowing high magnetic field operation with the field applied parallel to the chip. We observe a resonance signal between the first and third excited states of Gd spins S = 7/2 in a CaWO 4 crystal, relevant for state control in multi-level systems.Solid state spin-based qubits are studied for quantum computing due to their relatively long coherence time 1,2 . Typical implementations of these qubits are molecule-based magnets 3-6 , nitrogen-vacancy (NV) centers in diamond 7 and quantum spins in crystals 8-11 . These spin-based qubits are designed such that the spins are well separated in the crystal, leading to an increased decoherence time due to weak spin dipolar interactions.Among the rare-earth ions, S-state lanthanide ions doped in a crystal have a rich energy level structure due to their large spin. Multi-level systems are promising for implementing few-qubits algorithms 12 or as quantum memories [13][14][15][16] . For quantum technology applications, a higher sensitivity electron spin resonance (ESR) measurement is needed to be able to manipulate spins in mesoscopic crystals placed on superconducting chips [17][18][19][20][21] .Compared to other ultra-high sensitivity ESR measurements 22,23 , the use of Josephson junctions can increase significantly the spatial resolution of the magnetic detection while allowing an on-chip implementation. For instance, the magnetic signal of one nanoparticle is detectable if placed on the junction of a micrometer sized superconducting quantum interference device (micro-SQUID) 24 . We present a novel setup for ESR measurements, which combines the high spin sensitivity of an on-chip micro-SQUID and the flexibility of a coplanar waveguide for microwave excitation. Different dc-SQUID implementations were also used to detect molecular 25,26 and diluted 27 spins. In our case, the coupling of the two devices generates a cavity effect, which amplifies the microwave power seen by the spins. When using micro-SQUIDs, the samples are positioned close to their loop for increased sensitivity since the device a) Electronic mail: gy10c@my.fsu.edu b) Electronic mail: ic@magnet.fsu. edu FIG. 1. (color online) Scanning electron micrograph of the device and of the micro-SQUID (inset). The darker (blue) area is the coplanar waveguide with the two Ω-loop shortcircuits between the central line and the lateral ground planes. The microwave excitation is depicted by the curvy arrow and an in-plane field B0 is generated by an external coil. The SQUIDs share a common ground (sketched as a white rectangle). Each SQUID has one I − V line shown in green for clarity in their narrowest region.can work under in-plane magnetic fields in the range of ∼Tesla [28][29][30] .Using this s...

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confidence: 99%

Sensitive spin detection using an on-chip SQUID-waveguide resonator

Yue

Chen

Barreda

et al. 2017

Applied Physics Letters

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“…The area is ≈ 150 µm 2 and the effective sensing thickness can be estimated to be ∼ 1 µm [41]. This gives a ∼ 150 µm 3 = 0.15 pl sensing volume, comparable to the sensing volume of EPR using dc-SQUIDs [21] and the smallest sensing volume of EPR using superconducting resonators [10]. The spin ensemble used in the experiment has a concentration of 3.7 × 10 18 spins/cm 3 , which means ≈ 5.5 × 10 8 spins are located within our sensing volume.…”

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confidence: 67%

“…Using this value, we infer a measurement sensitivity of ≈ 1.5 × 10 4 spins, within the range of sensitivities of parametric-amplified pulsed EPR using typical superconducting lumped-element resonators [42,43]. The sensitivity is also about two orders of magnitude better than the sensitivity of EPR using dc-SQUIDs [21]. We note that the repetition time in our experiment were 20 times shorter than the repetition time in dc-SQUID EPR measurements, and thus we expect a factor of √ 20 ≈ 4.5 improvement in sensitivity from increased repetition rate.…”

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confidence: 75%

“…This method allows both magnetic field and frequency-dependent measurements. One typ- * rangga.budoyo@lab.ntt.co.jp ical magnetometer is a direct current-superconducting quantum interference device (dc-SQUID) [18][19][20], with continuous wave (cw)-EPR sensitivities reaching ∼ 10 6 spins/ √ Hz [21]. The stated sensitivity was limited by measurements using switching readout to obtain the critical current of the SQUID, which involves switching to voltage state and causes heating.…”

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confidence: 99%

“…In a JBA magnetometer, the junction is replaced by a dc-SQUID, thus the resonance is tunable by changing the flux penetrating the dc-SQUID [27]. The EPR sensitivity improvement was due to the increased detection sensitivity from operating in the bifurcation regime, as well as higher measurement repetition rates possible compared to switching measurements using dc-SQUIDs [21]. We used the JBA to perform cw-EPR on Er 3+ doped Y 2 SiO 5 (YSO) crystal.…”

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confidence: 99%

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Electron paramagnetic resonance spectroscopy ofEr3+:Y2SiO5using a Josephson bifurcation amplifier: Observation of hyperfine and quadrupole structures

Budoyo

Kakuyanagi

Toida

et al. 2018

Phys. Rev. Materials

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We performed magnetic field and frequency tunable electron paramagnetic resonance spectroscopy of an Er 3+ doped Y2SiO5 crystal by observing the change in flux induced on a direct currentsuperconducting quantum interference device (dc-SQUID) loop of a tunable Josephson bifurcation amplifer. The observed spectra show multiple transitions which agree well with the simulated energy levels, taking into account the hyperfine and quadrupole interactions of 167 Er. The sensing volume is about 0.15 pl, and our inferred measurement sensitivity (limited by external flux noise) is approximately 1.5 × 10 4 electron spins for a 1 s measurement. The sensitivity value is two orders of magnitude better than similar schemes using dc-SQUID switching readout.Electron paramagnetic resonance (EPR) is the gold standard tool to characterize the spin and magnetic properties of a wide range of materials [1,2]. Over several decades, there has been numerous efforts to improve the sensitivity of EPR measurements, including magnetic resonance force microscopy [3,4] and using a single NV center in diamond [5,6]. In recent years, significant improvements were achieved by operating in cryogenic temperatures, where thermal noise is significantly reduced and the spins are highly polarized. In such cases the spins of interest are coupled to superconducting planar resonators [7,8] or 3D cavities [9], resulting in avoided crossing or reduction of resonator quality factor. By combining superconducting lumped-element resonators with small magnetic mode volume and quantumlimited parametric amplifiers, recently sensitivity values of pulsed EPR have reached ∼ 60 spins/ √ Hz [10]. However, these EPR schemes typically only allow magnetic field-dependent study, because the operating frequency range is limited to frequencies near the resonator's resonance. Frequency and magnetic field-dependent EPR spctroscopy can be advantageous when compared to conventional, single-frequency EPR, in the characterization of more complicated materials [11][12][13], e.g., anisotropic materials, systems with electron spin S > 1/2 (zerofield interactions), or systems with nuclear spin I > 0 (hyperfine and quadrupole interactions). Efforts to extend the frequency range include using a tunable resonator [8,13,14], a resonator with multiple narrowly spaced modes (e.g., a whispering gallery mode resonator [15,16]), or a broadband waveguide [12,17]. However, these schemes typically suffer from worse sensitivity or still limited frequency range.EPR can also be performed by measuring the magnetization from the polarization of spins using a sensitive magnetometer. This method allows both magnetic field and frequency-dependent measurements. One typ- * rangga.budoyo@lab.ntt.co.jp ical magnetometer is a direct current-superconducting quantum interference device (dc-SQUID) [18][19][20], with continuous wave (cw)-EPR sensitivities reaching ∼ 10 6 spins/ √ Hz [21]. The stated sensitivity was limited by measurements using switching readout to obtain the critical current of the SQUID, which i...

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