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Silicon vacancies (Vsi) in silicon carbide (SiC) have attracted attention because they can be used for quantum sensors (F. Fuchs et al., Nat. Com. 6: 7578 (2015)). We aim to develop Vsi magnetic sensors operating at high temperatures because of its structural stability. However, change with temperatures, especially high temperature, in optically detected magnetic resonance (ODMR) in the ground state of Vsi, which is the basic principle of magnetic sensing, is less well understood. Here, we report the change in ODMR spectra of Vsi with different temperatures., Defects in solids for quantum technologies(DSQT)

Negatively charged silicon vacancy (VSi−) defects in silicon carbide are expected to be used for magnetic sensors under harsh environments, such as space and underground due to their structural stability and potential for high-fidelity spin manipulation at high temperatures. To realize VSi− based magnetic sensors operating at high temperatures, the temperature dependence of optically detected magnetic resonance (ODMR) in the ground states of VSi− defects, which is the basic principle of magnetic sensing, should be systematically understood. In this work, we demonstrate the potential of VSi− magnetic sensors up to at least 591 K by showing the ODMR spectra with different temperatures. Furthermore, the resonance frequency of the ground level was independent of temperature, indicating the potential for calibration-free magnetic sensors in temperature-varying environments. We also characterize the concentration of VSi− defects formed by electron irradiation and clarify the relationship of magnetic sensing sensitivity to VSi− concentration and find that the sensing sensitivity increases linearly with VSi− concentration up to at least 6.0 × 1016 cm−3. The magnetic sensitivity at a temperature above 549 K was reduced by half as compared to that at 300 K. The results pave the way for the use of a highly sensitive VSi−-based magnetic sensor under harsh environments.

炭化ケイ素中のシリコン空孔(Vsi)は、磁場や温度を高感度に検出できる「量子センサ」としての応用が期待されている。Vsiは高エネルギー電子線照射によって形成することができ、センサ感度はVsiの数(濃度)に依存するが、実用化のためにはVsi濃度の定量が重要となる。また、電子線照射によってデコヒーレンスの原因となる不要な照射欠陥も同時に形成されるため、その影響を明らかにするとともに低減する手法を確立する必要がある。本研究では、電子スピン共鳴(ESR)測定より、電子線照射量に対するVsi形成濃度を定量化するとともに、磁気センシングの基本原理である光検出磁気共鳴(ODMR)スペクトルの変化を調べ、照射欠陥の影響について検討した。高純度半絶縁性4H-SiC基板に2 MeV電子線を最大3.0×1018 cm-2まで照射し、Vsiを形成した。その後、真空中600℃で30分間の熱処理を行い、Vsi以外の不要な欠陥を低減した(Y. Chiba et al., Mater. Sci. Forum 1004, 337 (2020).) 。Fig.1(a)は3.0×10^18 cm-2照射した試料の室温でのESRスペクトルであり、(b)は室温ESR測定により同定した電子線照射量に対するVsi濃度の変化を示している。Vsi起因のESR信号は電子線照射量に対し比例関係にあると考えVsi収率を算出すると、未熱処理試料では5.7×10^(-3) cm^(-1) 、熱処理試料では3.6×10^(-3) cm^(-1) となった。講演では、Vsi濃度に対するODMRスペクトル（磁気感度）の変化について議論する。, 第69回応用物理学会春季学術講演会

電子線照射を用いればダイヤモンド中のNV（窒素・空孔）センターを高濃度に形成することが出来ることが知られている。2 MeV電子線照射を室温で実施し、照射を進める過程で熱処理を行い、その都度P1センター（格子中窒素不純物）の消費の様子や形成されたNVセンターの電荷状態、総量と照射量の関係を調べた。その結果、高効率でのNVセンター形成が確認出来た一方でP1センターがNVセンター以外の欠陥に消費されている可能性が示唆された。, 第69回応用物理学会春季学術講演会

炭化ケイ素(SiC)中のシリコン空孔(VSi)は磁気や温度を高感度に検出する「量子センサ」として注目されており、特に、VSiは高温下でも安定して存在するため、宇宙や地底といった厳環境に対応できる高感度磁気センサなどへの応用が期待できる。しかし、磁気センシングの基本原理となる光検出磁気共鳴(ODMR)現象の高温下での振る舞いは明らかになっていない。また、VSiは高エネルギー電子線照射によって形成するが、デコヒーレンスの要因となる不要な欠陥も同時に形成され、その影響も考慮しなければならない。そこで本研究では、ODMR スペクトルに対するVSi形成量及び測定温度依存性を系統的に調査した。さらに、磁気感度評価を行い、シリコン空孔量子センサの実現に向けた新たな知見を示した。, 第 11 回 半導体・超電導量子コテレンスと量子情報参加の為

Negatively charged boron vacancy (V B –) in hexagonal boron nitride has attracted attention as a promising spin defect for quantum sensing applications. Hence, a fabrication method for generation of V B – with superior spin properties would be desirable. In this study, we demonstrated V B – formation by two thermal treatment methods. Both methods improve the signal-to-noise ratio of optically detected magnetic resonance signal by a factor of 4. Furthermore, a zero-field splitting parameter E which reflects crystal distortion after irradiation significantly reduces for irradiation above 650 °C. These findings indicate that thermal treatment is an effective method for a V B – based quantum sensor.

Silicon vacancy (VSi) centers in silicon carbide have attracted attention because of their potential applications to quantum sensors (high-sensitivity magnetic field and temperature sensors). VSi centers are also expected to be used for magnetic sensors under harsh environments such as space and undergrounds, since they have structural stability and the potential of high-fidelity spin manipulation at high temperatures. To realize VSi based magnetic sensors operating at high temperature, understanding of optically detected magnetic resonance (ODMR) in the ground states of VSi centers, which is the basic principle of magnetic sensing, is crucial. In particular, the effects of temperature on the ODMR spectra are less well understood. Here, we demonstrate the potential of VSi magnetic sensors at high temperatures by showing the ODMR spectra with different temperatures. We also systematically investigate the effects of high energy electron irradiations on the ODMR spectra of formed VSi centers. The concentration of VSi centers increases with increasing electron irradiation dose, resulting in the enhancement of sensitivity, but the increase of undesired defects which might cause decoherence is also considered. Hence, the effects of electron irradiation dose should be clarified to obtain better sensitivity of VSi based magnetic sensors., The 4th International Forum on Quantum Metrology and Sensing

ダイヤモンド量子センサーの感度は、NVセンターの数が増えるほど向上する。そのため、高いセンサー感度を実現するためには、多数のNVセンターが必要となる。我々は、強く効果的なマイクロ波照射法や光励起法の開発により、多数のNVセンターを含む大きな体積のセンサーの制御や読み出しの効率を大幅に改善し、高感度なダイヤモンド量子センサーを開発することに成功した 。, QST高崎サイエンスフェスタ2021

The diamond NV center is expected to be applied to high-sensitivity quantum magnetic sensors. The excellent spin characteristics are derived from the physical properties of diamond as a high-temperature material, and it has already been reported that the spin coherence time at room temperature exceeds 2 ms. In order to improve the sensitivity, it is indispensable to improve the crystalline quality and appropriately form the NV centers. In this talk, we will focus on the research conducted at NIMS regarding diamond crystal growth for the purpose of quantum magnetic sensor application., NIMS WEEK

We investigated spin-echo coherence times T2 of negatively charged nitrogen vacancy center (NV−) ensembles in single-crystalline diamond synthesized by either the high-pressure and high-temperature and chemical vapor deposition methods. This study specifically examined the magnetic dipole–dipole interaction (DDI) from the various electronic spin baths, which are the source of T2 decoherence. Diamond samples with NV− center concentration [NV−] comparable to those of neutral substitutional nitrogen concentration [Ns0] were used for DDI estimation. Results show that the T2 of the ensemble NV− center decreased in inverse proportion to the concentration of nitrogen-related paramagnetic defects [NPM], being the sum of [Ns0], [NV−], and [NV0], which is a neutrally charged state NV center. This inversely proportional relation between T2 and [NPM] indicates that the nitrogen-related paramagnetic defects of three kinds are the main decoherence source of the ensemble NV− center in the single-crystalline diamond. We found that the DDI coefficient of NVH− center was significantly smaller than that of Ns0, the NV0 center, or the NV− center. We ascertained the DDI coefficient of the NV− center [Formula: see text] through experimentation using a linear summation of the decoherence rates of each nitrogen-related paramagnetic defect. The obtained value of 89 μs ppm for [Formula: see text] corresponds well to the value estimated from the relation between DDI coefficient and spin multiplicity.

電子線照射を用いればダイヤモンド中のNV（窒素・空孔）センターを高濃度に形成することが出来ることが知られているが、照射中加熱することでより効率の良い形成が可能となることから、2 MeV電子線照射を室温、800℃及び1000℃中にて実施した。P1センター（格子中窒素不純物）の消費の様子や形成されたNVセンターの電荷状態、総量と照射量の関係を調べた。その結果、高温中での照射によりNVセンター形成効率が改善され、特に800℃においてその効果が高いことが分かった。, 量子生命科学会第3回大会

炭化ケイ素(SiC)中のシリコン空孔(VSi−)は磁気や温度を高感度に検出する「量子センサ」として注目されており、特に、VSi−は高温下でも安定して存在するため、宇宙や地底といった厳環境に対応できる高感度磁気センサなどへの応用が期待できる。しかし、磁気センシングの基本原理となる光検出磁気共鳴(ODMR)現象の高温下での振る舞いは明らかになっていない。また、VSi−は高 エネルギー電子線照射によって形成するが、デコヒーレンスの要因となる不要な欠陥も同時に形成され、その影響も考慮しなければならない。そこで本研究では、ODMR スペクトルに対するVSi−形成量及び測定温度依存性を系統的に調査した。高純度半絶縁性4H-SiC 基板に2 MeV 電子線を照射してVSi−を形成した。その後、真空中600 ℃で30 分間の熱処理を行い、VSi−以外の不要な欠陥を低減した。その脚気、70 MHz に基底準位のゼロ磁場分裂に起因する共鳴ピークが確認できた。しかし、高温ではコントラスト(ピーク高)が低下すると共に半値幅が増加したため、磁気感度は低下することが予想される。, 第82回応用物理学会秋季学術講演会

SiCデバイス中に作製したシリコン空孔量子センサーを用いて電流誘起磁場を直接測定した, 応用物理学会秋季学術講演会

1. Introduction Negatively charged nitrogen-vacancy (NV-) center in diamond is expected as quantum sensor to measure small changes in physical quantities, such as magnetic and electric field, temperature, strain, etc. The quantum sensors with high sensitivity require diamond containing high concentration of NV centers. Electron irradiation is a good method to create high concentration of NV centers. The high energy electrons knock carbon atoms out of the diamond lattice, creating vacancies. Annealing an irradiated diamond causes all the vacancies to become mobile and subsequently trapped by substituted nitrogen (P1 centers), forming NV centers. It is known that the process of NV center creation depends on the initial P1 concentrations, and the irradiation fluence dependence at low initial P1 concentrations below 1 ppm is still uncleared. In this study, we irradiate samples with different initial P1 concentrations, especially low concentration, and estimate the fluence dependency of the charge state and the amount of created NV centers. 2. Experiments The diamonds synthesized by High Pressure and High Temperature (HPHT) and Chemical Vapor Deposition (CVD) were used. The initial concentration of P1 was in the range from 40 ppb to 100 ppm. 2 MeV electrons were irradiated with a fluence up to 2E18 cm-2 at room temperature. Then, the samples were annealed at 1000℃ for 2 hours to create NV center. The concentration of P1 was measured by Electron Spin Resonance (ESR) using JES-X330 (JEOL). The ratio between NV0 and NV- was estimated from photoluminescence (PL) spectrum measurement obtained using LabRAM HR Evolution (HORIBA). All these measurements were performed at room temperature. 3. Results & Discussion In the case of type Ib HPHT diamond containing initial P1 concentration of ~100 ppm, the most of NV centers are thought to be NV-, and PL measurement revealed that only NV- was detected when the fluence of 2E18 cm-2. P1 center acts as electron donor, and provide electron to NV0. In contrast to high P1 concentration, an appreciable fraction of NV center is present as NV0 for samples with low initial P1 concentration (~ 10 ppm). We examined the relationship between the concentration of P1 and the fluence, using HPHT diamonds with initial P1 concentration of ~0.8 ppm. The concentration of P1 decreased to ~0.3 ppm when the fluence of 1.5E17 cm-2. This result suggests that P1 centers of ~0.5 ppm change to either NV center or positively charged substitutional nitrogen. PL spectrum when the fluence of 1.5×1017 cm-2, shows that both NV0 and NVare created. The ratio of NV- to NV0 decreased as irradiation fluence, to be 0.70 after irradiated with 1.0×1017 cm-2 and 0.53 after irradiated with 1.5E17 cm-2. It is noted that NV0 was formed even though P1 center which can act as electron donor to NV0 center remains. Similar results were observed for CVD diamonds with initial P1 concentration of ~40 ppb. The adequate fluence to maximize NV- concentration for diamonds containing low P1 concentration will be discussed by examining the fluence dependency of the charge state and total amount of NV center., New Diamond and Nano Carbons 2020/2021

広帯域の交差コプレーナー導波路を用いてT2*を伸長した結果を報告する。, 第68回 応用物理学会春季学術講演会

The nitrogen-vacancy (NV) center in diamond is extensively studied for a next-generation high-sensitivity magnetometer. The DC magnetic sensitivity can be improved by extending the inhomogeneous spin dephasing time through suppressing the effects of inhomogeneous fluctuations or by increasing the number of effective NV centers through expanding the sensor volume. It has been demonstrated that strain-induced dephasing can be suppressed by double quantum (DQ) technique with two-tone microwaves (MW), and spin bath-induced dephasing can be suppressed by spin bath drive (SBD) technique with multi-tone radio-frequency (RF) to drive the P1 centers. To combine these T2* -extension techniques with a bulk diamond, it is necessary to apply MW and RF uniformly to the sample. A coplanar waveguide (CPW) circuit has been reported to be useful for uniform microwave irradiation to a bulk sample. In this study, we reports the newly designed and fabricated a cross-aligned two-layer CPW circuit., 3rd IFQMS

Introduction Negatively charged nitrogen-vacancy (NV-) center in diamond is known as quantum sensor, can be used to measure small changes in physical quantities, such as magnetic field and temperature. To enhance the sensitivity of the quantum sensor, increasing NV- and decreasing neutral charge state NV0 in diamonds are needed since NV0 does not act as quantum sensor. The electron irradiation is a good method to create high concentration of NV centers. The high energy electrons create vacancies in diamond. Annealing allows the vacancies to move and to be trapped by substitutional nitrogen (P1 centers), forming NV centers. In this study, we irradiate diamonds containing different initial P1 concentrations with electrons and evaluate the fluence dependence of the charge state and the amount of created NV centers, for the purpose of determining appropriate fluence to form NV centers efficiently. Method The commercial diamonds synthesized by High Pressure and High Temperature (HPHT) were used. 2 MeV electrons were irradiated with fluences up to 3×1018 cm-2 at room temperature. Then, the samples were annealed at 1000℃ for 2 hours to create NV centers. The concentration of P1 (number of electron spins) was measured by Electron Spin Resonance (ESR). The initial concentration of P1 was in the range from 50 ppm to 100 ppm. The ratio of NV- to NV0 was evaluated from photoluminescence (PL) spectrum. All these measurements were performed at room temperature. Results & Discussion The concentration of P1 decreased with increasing fluence. In contrast, total amount of NV centers increased with increasing fluence and only NV- was detected when the fluence of 3×1018 cm-2. The result suggests that remained P1 centers act as electron donor, and provide electron to NV0. Further irradiation with higher fluence will be needed to achieve the adequate one to maximize NV- concentration for diamonds remaining the charge state only in NV-., 3rd IFQMS

温度と磁場を分離計測可能であり、車載電池応用や生体計測応用に有効である計測技術を発表する, 2020年 第81回応用物理学会秋季学術講演会

We study the application of a counter-diabatic driving (CD) technique to enhance the thermodynamic efficiency and power of a quantum Otto refrigerator based on a superconducting qubit coupled to two resonant circuits. Although the CD technique is originally designed to counteract non-adiabatic coherent excitations in isolated systems, we find that it also works effectively in the open system dynamics, improving the coherence-induced losses of efficiency and power. We compare the CD dynamics with its classical counterpart, and find a deviation that arises because the CD is designed to follow the energy eigenbasis of the original Hamiltonian, but the heat baths thermalize the system in a different basis. We also discuss possible experimental realizations of our model., Comment: 9 pages, 8 figures

Energy conservation and battery life extension are key challenges for the next-generation hybrid electric vehicles. In particular, the temperature and electric currents in a storage battery need to be monitored simultaneously with ∼1 kHz signal bandwidth for optimum battery usage. Here we introduce a centimeter-scale portable quantum sensor head, consisting of a diamond substrate hosting an ensemble of nitrogen-vacancy (NV) color centers with a density of ∼3 × 1017 cm−3. One diamond surface is attached to a multi-mode fiber for simultaneous optical excitation and readout of the NV centers, while the other diamond surface is attached to a coplanar microwave guide for NV spin ground-state mixing. Signal bandwidth of 1 kHz was realized through time-domain multiplexing of the two-tone microwave frequency modulation at 20 kHz. Two microwave frequencies were locked to the two resonance points that were determined from the optically detected magnetic resonance spectrum. From the mean and the difference of the deviation from the two locked frequencies, the temperature and magnetic field were obtained simultaneously and independently, with sensitivities of 3.5 nT/Hz1/2 and 1.3 mK/Hz1/2, respectively. We also showed that our sensor reached a minimum detectable magnetic field of 5 pT by accumulating signals for over 10 000 s.

We characterized the excited state (ES) and the ground state (GS) of negatively charged silicon vacancy ( V Si −) centers in hexagonal silicon carbide (4H-SiC) using optically detected magnetic resonance (ODMR) to realize thermometric quantum sensors. We report the observation of inverted contrast between ODMR signals of the ES and the GS and clarify the effect of energy sublevels of spin states in 4H-SiC. We confirm that ES ODMR signals of V Si − centers are dependent on the temperature with a thermal shift of 2 MHz/K on zero-field splitting (ZFS). Thus, we fabricated microscale dots of V Si − centers in a 4H-SiC p–n diode using proton beam writing and demonstrated the operation of thermometric quantum sensors by measuring the temperature change induced by an injected current. Our demonstration paves the way for the development of atomic-size thermometers inside SiC power devices for future applications.

We have developed the magnetic probe with a diamond quantum sensor and electromagnetic coils to detect sentinel lymph nodes (SLNs), as the medical application of diamond quantum sensing. The probe magnetizes magnetic nanoparticles (MNPs) accumulated in SLNs and detect the magnetic fields of magnetized MNPs. In this study. We designed a ferromagnetic core that has a unique shape and optimized the magnetic field generation system for improving the detection performance, such as the magnetic sensitivity and detectable distance. The proposed magnetic core enhances an excitation magnetic field strength at a longer distance and suppresses a bias field strength at a location of the diamond quantum sensor. The increment of the excitation field is approximately 370% and the decrement of the bias field is approximately 45%. In addition to the proposed magnetic core, even applying a cancellation coil, the excitation field strength is ten-fold compared with the coil only structure, suggesting the larger magnetization of MNPs generates the large magnetic field for longer detectable distance.

We have developed the magnetic probe with a diamond quantum sensor and electromagnetic coils to detect sentinel lymph nodes (SLNs), as the medical application of diamond quantum sensing. The probe magnetizes magnetic nanoparticles (MNPs) accumulated in SLNs and detect the magnetic fields of magnetized MNPs. In this study, we designed a ferromagnetic core that has a unique shape and optimized the magnetic field generation system for improving the detection performance such as the magnetic sensitivity and detectable distance. The proposed magnetic core enhances an excitation magnetic field strength at a longer distance and suppresses a bias field strength at a location of the diamond quantum sensor. The increment of the excitation field is approximately 370% and the decrement of the bias field is approximately 45%. In addition to the proposed magnetic core, even applying a cancellation coil, the excitation field strength is tenfold compared with the coil only structure, suggesting the larger magnetization of MNPs generates the large magnetic field for longer detectable distance.

Information thermodynamics bridges information theory and statistical physics by connecting information content and entropy production through measurement and feedback control. Maxwell’s demon is a hypothetical character that uses information about a system to reduce its entropy. Here we realize a Maxwell’s demon acting on a superconducting quantum circuit. We implement quantum non-demolition projective measurement and feedback operation of a qubit and verify the generalized integral fluctuation theorem. We also evaluate the conversion efficiency from information gain to work in the feedback protocol. Our experiment constitutes a step toward experimental studies of quantum information thermodynamics in artificially made quantum machines., Maxwell’s demon is a hypothetical character that uses information about a system to reduce its entropy, highlighting the link between information and thermodynamic entropies. Here the authors experimentally realise a Maxwell's demon controlling a quantum system and explore how it affects thermodynamic laws.

A superconducting qubit in the strong dispersive regime of a circuit quantum electrodynamics system is a powerful probe for microwave photons in a cavity mode. In this regime, a qubit spectrum is split into multiple peaks, with each peak corresponding to an individual photon number in the cavity (discrete ac Stark shift). Here, we measure the qubit spectrum in the cavity that is driven continuously with a squeezed vacuum field generated by a Josephson parametric amplifier. By fitting the qubit spectrum with a model which takes into account the finite qubit excitation power, the photon number distribution, which is dissimilar from the apparent peak area ratio in the spectrum, is determined. The photon number distribution shows the even-odd photon number oscillation and quantitatively fulfills Klyshko's criterion for the nonclassicality., Comment: 10 pages, 11 figures, 1 table

We developed a novel magnetometer that employs negatively charged nitrogen-vacancy (NV−) centers in diamond, to detect the magnetic field generated by magnetic nanoparticles (MNPs) for biomedical applications. The compact probe system is integrated into a fiber-optics platform allowing for a compact design. To detect signals from the MNPs effectively, we demonstrated, for the first time, the application of an alternating current (AC) magnetic field generated by the excitation coil of several hundred microteslas for the magnetization of MNPs in diamond quantum sensing. In the lock-in detection system, the minimum detectable AC magnetic field (at a frequency of 1.025 kHz) was approximately 57.6 nT for one second measurement time. We were able to detect the micromolar concentration of MNPs at distances of a few millimeters. These results indicate that the magnetometer with the NV− centers can detect the tiny amounts of MNPs, thereby offering potential for future biomedical applications.

We developed a novel magnetometer that employs negatively charged nitrogen-vacancy (NV–) centers in diamond, to detect the magnetic field generated by magnetic nanoparticles (MNPs) for biomedical applications. The compact probe system is integrated into a fiber-optics platform allowing for a compact design. To detect signals from the MNPs effectively, we demonstrated, for the first time, the application of an alternating current (AC) magnetic field generated by the excitation coil of several hundred microteslas for the magnetization of MNPs in diamond quantum sensing. In the lock-in detection system, the minimum detectable AC magnetic field (at a frequency of 1.025 kHz) was approximately 57.6 nT for one second measurement time. We were able to detect the micromolar concentration of MNPs at distances of a few millimeters. These results indicate that the magnetometer with the NV- centers can detect the tiny amounts of MNPs, thereby offering potential for future biomedical applications.

Ultimate sensitivity for quantum magnetometry using nitrogen-vacancy (NV) centers in a diamond is limited by a number of NV centers and coherence time. Microwave irradiation with a high and homogeneous power density for a large detection volume is necessary to achieve a highly sensitive magnetometer. Here, we demonstrate a microwave resonator to enhance the power density of the microwave field and an optical system with a detection volume of 1.4 × 10−3 mm3. The strong microwave field enables us to achieve 48 ns Rabi oscillation which is sufficiently faster than the phase relaxation time of NV centers. This system combined with a decoupling pulse sequence, XY16, extends the spin coherence time (T2) up to 27 times longer than that with a spin echo method. Consequently, we obtained an AC magnetic field sensitivity of 10.8 pt/Hz using the dynamical decoupling pulse sequence.

We analyze the stochastic evolution and dephasing of a qubit within the quantum jump (QJ) approach. It allows one to treat individual realizations of inelastic processes, and in this way it provides solutions, for instance, to problems in quantum thermodynamics and distributions in statistical mechanics. As a solvable example, we study a qubit in the weak dissipation limit, and demonstrate that dephasing and relaxation render the Jarzynski and Crooks fluctuation relations (FRs) of non-equilibrium thermodynamics intact. On the contrary, the standard two-measurement protocol, taking into account only the fluctuations of the internal energy $U$, leads to deviations in FRs under the same conditions. We relate the average $\langle e^{-\beta U} \rangle $ (where $\beta$ is the inverse temperature) with the qubit's relaxation and dephasing rates, and discuss this relationship for different mechanisms of decoherence., Comment: 9 pages

We investigate controlled phase separation of a binary Bose-Einstein condensate (BEC) in the proximity of mixed-spin-channel Feshbach resonance in the |F = 1, mF = +1> and |F = 2,mF = -1> states of 87Rb at a magnetic field of 9.10 G. Phase separation occurs on the lower magnetic-field side of the Feshbach resonance while the two components overlap on the higher magnetic-field side. The Feshbach resonance curve of the scattering length is obtained from the shape of the atomic cloud by comparison with the numerical analysis of coupled Gross-Pitaevskii equations., 6 pages, 5 figures