quantum spintronics design - keio university › itoh_group › abe › pdf › cmd35.pdf ·...
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Quantum Spintronics Design (NV centers in diamond)
Eisuke Abe RIKEN Center for Emergent Matter Science
2019.09.04 CMD Spintronics Design Course
@Osaka University
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Short CV
©Google Earth
2001.4 – 2006.3 (Keio) → Quantum computing (silicon)
2010.1 – 2011.6 (Oxford) → Hybrid system (spin–cavity coupling)
2006.4 – 2009.12 (ISSP, UT) → Quantum transport (GaAs QDs, Josephson)
2011.7 – 2015.3 (Stanford/RIKEN) → Quantum network (InAs QDs)
2015.4 – 2019.1 (Keio) → Quantum sensing (diamond)
2019.2 – Present (RIKEN) → Quantum computing (Josephson)
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Diamond envy
©Lucara Diamond
1109 carats, $70M
ρN = 1.77 x 1023 cm-3 C
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Diamond NV
N V
C
©Lucara Diamond
1109 carats, $70M
ρN = 1.77 x 1023 cm-3
S = 1
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Diamond NV
N V
C ρN = 1.77 x 1023 cm-3
22 x 0.5 mm3, $700 (E6) [N] < 5 ppb, [NV] < 0.03 ppb
S = 1
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Why a single NV spin?
• Optically active (init. & readout) • Microwave spin control • High coherence (LT–RT–500 K)
[Biology] Annu. Rev. Phys. Chem. 65, 83 (2014) Schirhagl et al. [Magnetometry] Rep. Prog. Phys. 77, 056503 (2014) Rondin et al.
[Magnetic resonance] J. Mag. Res. 269, 225 (2016) Wrachtrup et al. [Quantum technologies] Nature Photon. 12, 516 (2018) Awschalom et al.
[Quantum internet] Science 362, eaam9288 (2018) Wehner et al.
Quantum sensing & Quantum network
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Nuclear spin
Diamond substrate
NV spin
Molecule
Quantum sensing
• Room T. operation • High spatial resolution • Nondestructive
• Nano MRI
ND
Living cell
Magnetic structure
Nano-tip
• Various modalities • Probe for CM systems • Biology
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Quantum network
Spin–spin entanglement between distant NVs
Nature 526, 682 (2015) Hensen et al.
Times Cited: 1210 (Google Scholar)
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Outline
• Basics of NV centers in diamond – Structure – Optical properties – Spin properties
• Quantum sensing
– Basics – Correlation spectroscopy and detection of nuclear spins – Ultrahigh resolution sensing – Determination of the position of a single nuclear spin
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Outline
• Basics of NV centers in diamond – Structure – Optical properties – Spin properties
• Quantum sensing
– Basics – Correlation spectroscopy and detection of nuclear spins – Ultrahigh resolution sensing – Determination of the position of a single nuclear spin
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Crystal & energy level structures • Negatively-charged (NV−) • 4 sp3 orbitals, 6 e− (5 from the defect, 1 captured) • C3v (symmetry axis = quantization axis)
a’1
a1
ex ey
Effective spin-1 system (e2-hole spin-triplet)
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Optical transitions C.B. (Eg = 5.47 eV = 227 nm)
V.B.
|e⟩
2.87 GHz |g⟩ ms = 0
ms = ±1
637 nm
515 nm
a’1
a1
ex ey
(e2-hole)
a’1
a1
ex ey
(ae-hole)
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PL spectroscopy C.B. (Eg = 5.47 eV = 227 nm)
V.B.
|e⟩
2.87 GHz |g⟩ ms = 0
ms = ±1
637 nm
515 nm
ZPL and PSB
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PL imaging C.B. (Eg = 5.47 eV = 227 nm)
V.B.
|e⟩
2.87 GHz |g⟩ ms = 0
ms = ±1
637 nm
515 nm
Count rate (cps)
Bright spot... single NV? 600–800 nm
2.5 μm x 2.5 μm
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Photon statistics
One photon at a time
|e⟩
2.87 GHz |g⟩ ms = 0
ms = ±1
637 nm
515 nm
C.B. (Eg = 5.47 eV = 227 nm)
V.B.
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Non-radiative path
|e⟩
2.87 GHz |g⟩ ms = 0
ms = ±1
637 nm
515 nm
1042 nm
C.B. (Eg = 5.47 eV = 227 nm)
V.B.
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Time-resolved fluorescence
|e⟩
2.87 GHz |g⟩ ms = 0
ms = ±1
637 nm
515 nm
1042 nm
C.B. (Eg = 5.47 eV = 227 nm)
V.B.
mS = 0
mS = −1
Difference
The NR channel provides a means to read out and initialize the NV spin
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CW ODMR
|e⟩
2.87 GHz |g⟩ ms = 0
ms = ±1
637 nm
515 nm
1042 nm
C.B. (Eg = 5.47 eV = 227 nm)
V.B.
Time
Laser
MW
SPCM
(Sweep frequency)
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CW ODMR at B0 = 0
|e⟩
2.87 GHz |g⟩ ms = 0
ms = ±1
637 nm
515 nm
1042 nm
C.B. (Eg = 5.47 eV = 227 nm)
V.B.
𝐻 = 𝐷𝑆𝑧2 Zero-field splitting
ms = 0 ↔ ±1
D = 2.87 GHz
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CW ODMR at B0 > 0
|e⟩
2.87 GHz |g⟩ ms = 0
ms = ±1
637 nm
515 nm
2γB0
B0 ‖ NV-axis
C.B. (Eg = 5.47 eV = 227 nm)
V.B.
𝐻 = 𝐷𝑆𝑧2 + 𝛾e𝐵0𝑆𝑧 Zeeman
γe = 28 MHz/mT
ms = 0 ↔ −1 ms = 0 ↔ 1
B0 = 4.7 mT (2.87±0.132 GHz)
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Experimental setup
Stripline & XYZ-piezo stage
Diamond
Objective
Amplifier
2.87 GHz
Vector SG AWG
100 MHz (IQ)
Permanent magnet & XYZ-translation stage
AOM
Laser
HWP
QWP
PBS
515 nm
Dichroic BS
Fiber coupler
SPCM
600–800 nm
Spectrometer
SPCM
Timing analyzer
(XY-galvo + Z-piezo & 1-axis magnet)
(Fiber laser& fiber AOM)
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Experimental setup
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Experimental setup
200 mm
380 mm
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Qubit & coherence
"0" ≡ 𝑚𝑠 = 0 "1" ≡ 𝑚𝑠 = −1
T2: measure of how long a superposition state is preserved
Ψ = 𝛼 0 + 𝛽|1⟩
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Magnetic environment
ρN = 1.77 x 1023 cm-3
[N] < 5 ppb, [NV] < 0.03 ppb
12C (I = 0) : 13C (I = ½) = 98.9% : 1.1%
14N (I = 1) : 15N (I = ½) = 99.6% : 0.4%
14N
13C
12C
V
14N (P1)
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Rabi oscillation Microwave
Tp
Initialization Readout
π-pulse π/2-pulse
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Pulsed ODMR Change fmw
Long (narrowband) π-pulse
Initialization Readout
Tp = 1292 ns
2.87 GHz
ms = 0
ms = ±1 2γB0
2.1 MHz 2.1 MHz
mI = −1 mI = 0 mI = 1
14N (I = 1)
Hyperfine coupling with 14N nucleus of the NV center itself
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Ramsey interference
t = 0 t = τ
π/2-pulse (x) π/2-pulse (x)
π/2 π/2
τ
Initialization Readout
Tπ/2 = 31.5 ns fosc = 2.1 MHz T2* = 0.50 μs
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Spin echo
Sign of phase accumulation
Phase accumulation by DC field
Positive
Negative
π/2 π/2 Initialization Readout
τ
π
τ
t = 0 t = τ(−) t = τ(+) t = 2τ
π-pulse (y) π/2-pulse (x) π/2-pulse (-x)
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Spin echo π/2 π/2
Initialization Readout
τ
π
τ
“Collapse and revival”
• Interaction with the nuclear spin bath ([13C] = 1.1%) • fc = γCB0 = 10.705 kHz/mT x 4.7 mT = 50.3 kHz • Revival at 2nτ = 2n/fc = 41.8 x n μs
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Spin echo π/2 π/2
Initialization Readout
τ
π
τ
T2 = 364 μs
“Collapse and revival”
• Interaction with the nuclear spin bath ([13C] = 1.1%) • fc = γCB0 = 10.705 kHz/mT x 4.7 mT = 50.3 kHz • Revival at 2nτ = 2n/fc = 41.8 x n μs
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Coherence time
exp −2𝜏𝑇2
𝑝
Stretched exponential decay
T2 = 71 μs p = 1.3
CVD growth of shallow single NV centers • Hydrogen-terminated • ~5 nm from the surface • [12C] = 99.999%
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Outline
• Basics of NV centers in diamond – Structure – Optical properties – Spin properties
• Quantum sensing
– Basics – Correlation spectroscopy and detection of nuclear spins – Ultrahigh resolution sensing – Determination of the position of a single nuclear spin
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Nuclear spin
Diamond substrate
NV spin
Molecule
Quantum sensing
• Room T. operation • High spatial resolution • Nondestructive
• Nano MRI
ND
Living cell
Magnetic structure
Nano-tip
• Various modalities • Probe for CM systems • Biology
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Nuclear spin sensing
Ext.
field
B0
Nuclear spins precess at fac = a few kHz–MHz under B0
Detect using quantum coherence
Weak AC magnetic field on the NV spin (11 nT@dNV = 5 nm)
fac Nuclear spin
Diamond substrate
NV spin
Molecule
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AC magnetometry CP (N = 4) π/2
τ/2 τ τ τ τ/2
π π π π π/2
Sign of phase accumulation
π AC field at fac = 1/2τ
Bac
Rev. Mod. Phys. 89, 035002 (2017) Degen et al.
𝛾𝐵ac� cos 2𝜋𝑓ac𝑡𝑡
0𝑑𝑡 φ = 8τγBac/π
Sensor phase buildup = decrease of coherence
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CP (N = 4) π/2
τ/2 τ τ τ τ/2
π π π π π/2
Sign of phase accumulation
AC field at fac ≠ 1/2τ
Multiple oscillations between π-pulses average out the sensor phase
Rev. Mod. Phys. 89, 035002 (2017) Degen et al.
AC magnetometry
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Nuclear spin sensing
• Single NV center in a natural abundant diamond ([13C] = 1.1%, dNV ~ 50 μm) • Sweep τ & repeat (f = 1/2τ, Δτ = 31.3 ns, N = 16) • fc = γCB0 = 10.705 kHz/mT x 36.2 mT
fc = 387.5 kHz
Phys. Rev. B 98, 121405 (2018) Sasaki et al.
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Correlation spectroscopy AC field at fac
Accumulate more phase if tcorr = m/fac
tcorr ts = Nτ
α1 α2
Nature Commun. 4, 1651 (2013) Laraoui et al. Phys. Rev. Appl. 4, 024004 (2015) Kong et al.
Nature Commun. 6, 8527 (2015) Staudacher et al. Phys. Rev. Lett. 116, 197601 (2016) Boss et al.
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Correlation spectroscopy AC field at fac
𝑝 𝑡1 ≈12 1 −
12𝛾𝐵ac𝑡s𝜋
2cos(2𝜋𝑓ac𝑡corr )
The transition probability for random phases
No gain of the phase if tcorr = (m+1/4)/fac
Sensor is in |ms = 0⟩,|−1⟩ (T1 limited)
tcorr ts = Nτ
α1 α2
Nature Commun. 4, 1651 (2013) Laraoui et al. Phys. Rev. Appl. 4, 024004 (2015) Kong et al.
Nature Commun. 6, 8527 (2015) Staudacher et al. Phys. Rev. Lett. 116, 197601 (2016) Boss et al.
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Correlation spectroscopy AC field at fac
Sensor is in |ms = 0⟩,|−1⟩ (T1 limited)
tcorr ts = Nτ
α1 α2
• ft = 1/2τ = 301.6 kHz • τ = 1.7875 μs
Where to look at?
Phys. Rev. B 98, 121405 (2018) Sasaki et al.
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Correlation spectroscopy of a nucleus
f1 = 215.6 kHz f0 = 387.5 kHz
No decay up to 100 μs
Phys. Rev. B 98, 121405 (2018) Sasaki et al.
f1 = 215.6 kHz f0 = 387.5 kHz
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Correlation spectroscopy of a nucleus
𝐻 = 𝑓c𝐼𝑧 + 𝑚𝑠 = −1 ⟨−1|(𝐴∥𝐼𝑧 + 𝐴⊥𝐼𝑥)
Hamiltonian of NV–13C coupled system
→ No hyperfine field when |ms = 0⟩
Phys. Rev. B 98, 121405 (2018) Sasaki et al.
f1 = fc + A’‖ (ms = −1) f0 = fc (ms = 0)
A’‖ = −171.9 kHz (f0 + f1)/2 = 301.55 kHz → dip
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Coherent control of a nuclear spin
𝐻 = 𝑓c𝐼𝑧 + 𝑚𝑠 = −1 ⟨−1|(𝐴∥𝐼𝑧 + 𝐴⊥𝐼𝑥)
Hamiltonian of NV–13C coupled system
Phys. Rev. B 98, 121405 (2018) Sasaki et al.
→ The single 13C n-spin rotates about the A⊥ axis
𝜏 ≈ 𝑓c +𝐴∥2
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Conditional rotation of a nuclear spin CP (N = 4) π/2
τ/2 τ τ τ τ/2
π π π π π/2
Q-axis of n-spin
|ms = 0⟩ |ms = −1⟩
Evolution of n-spin vector
Start from |ms = 0⟩ Start from |ms = −1⟩
z
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𝑃X = 1 −12
(1 − 𝒏0 ⋅ 𝒏−1) sin2𝑁𝜙cp
2
Coherent control of a nuclear spin
fcp = 10.2 kHz ≈ A’⊥/2 PX < 0.5 → single
Phys. Rev. B 98, 121405 (2018) Sasaki et al.
Transition probability of the NV spin
Phys. Rev. Lett. 109, 137602 (2012) Taminiau et al.
−1
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Determination of hf constants
𝐴∥ ∝3 cos2 𝜃 − 1
𝑟3 𝐴⊥ ∝
3 cos 𝜃 sin𝜃𝑟3
Magnetic dipole int.
A‖ = −173.1 kHz A⊥ = 22.3 kHz
+ contact hf int.
A‖ = −175.1±2.1kHz A⊥ = 21.9±0.2 kHz
DFT: New J. Phys. 20, 023022 (2018) Nizovtsev et al.
(r, θ) = (6.84 Å, 94.8o) Phys. Rev. B 98, 121405 (2018) Sasaki et al.
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Toward single-molecular imaging
• Information of the positions of the individual nuclei → Accurate measurement of e–n int. const’s (A∥, A⊥) ≈ (r, θ) → Lack of information on the azimuthal angle ϕ
• Spectral resolution → Easy to resolve isotopes → Need to measure J-couplings & chemical shifts (ppm!) → Limited by sensor/memory lifetimes (T2e/n, T1e/n)
Nuclear spin
NV spin
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Toward single-molecular imaging
• Information of the positions of the individual nuclei → Accurate measurement of e–n int. const’s (A∥, A⊥) ≈ (r, θ) → Lack of information on the azimuthal angle ϕ
• Spectral resolution → Easy to resolve isotopes → Need to measure J-couplings & chemical shifts (ppm!) → Limited by sensor/memory lifetimes (T2e/n, T1e/n)
Nuclear spin
NV spin
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AC magnetometry CP (N = 4) π/2
τ/2 τ τ τ τ/2
π π π π π/2
Sign of phase accumulation
AC field at fac = 1/2τ φ = 8γBacτ/π
φ = 0
• φ depends on the initial phase α of the AC field (φ ∝ cos α)
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AC magnetometry AC field at fac
α1
ts = Nτ
α2 α3 α4 α5
• φ depends on the initial phase α of the AC field (φ ∝ cos α) • Average over random α
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Ultrahigh resolution sensing AC field at fac
tL
I(α1) I(α2) I(α3) I(α4) I(α5)
Science 356, 832 (2017) Schmitt et al.; Science 356, 837 (2017) Boss et al.; Nature 555, 351 (2018) Glenn et al.
α1
ts = Nτ
α2 α3 α4 α5
• φ depends on the initial phase α of the AC field (φ ∝ cos α) • Average over random α • If the data acq. is periodic, adjacent α’s are related by αk+1 = 2π factL+ αk
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Ultrahigh resolution sensing AC field at fac
tL
I(α1) I(α2) I(α3) I(α4) I(α5)
LO
Science 356, 832 (2017) Schmitt et al.; Science 356, 837 (2017) Boss et al.; Nature 555, 351 (2018) Glenn et al.
α1
ts = Nτ
α2 α3 α4 α5
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Ultrahigh resolution sensing
T = 300 sec FWHM = 3.73 mHz
T = 900 sec FWHM = 1.22 mHz
T = 1800 sec FWHM = 0.601 mHz
T = 3600 sec FWHM = 0.304 mHz
J. Appl. Phys. 123, 161101 (2018) Abe & Sasaki
Bac = 96.5 nT & fac = 2.001 MHz applied from a coil, detected by a single NV center
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Ultrahigh resolution sensing
FWHM = T −1 (not a fit)
SNR ∝ T 0.5
J. Appl. Phys. 123, 161101 (2018) Abe & Sasaki
• Spectral resolution not limited by sensor/memory lifetimes (T2e/n, T1e/n) • Only limited by the stability of LO (essentially infinite) • Resolution = T −1 & SNR ∝ T 0.5 → Precision ∝ T −1.5
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NMR spectroscopy
See also: Science 357, 67 (2017) Aslam et al. (Wrachtrup, Stuttgart) [B0 = 3 T, fe = 87 GHz, T1n = 260 s]
• [NV] ≈ 3 x 1017 cm−3
• # of NV ≈ 5 x 109 • Vdetect ≈ 25 pL • # of protons ≈ 2.5 x 1015
• RF pulse → FID
Data from Harvard: Nature 555, 351 (2018) Glenn et al.
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NMR spectroscopy
See also: Science 357, 67 (2017) Aslam et al. (Wrachtrup, Stuttgart) [B0 = 3 T, fe = 87 GHz, T1n = 260 s]
Data from Harvard: Nature 555, 351 (2018) Glenn et al.
J-coupling Chemical shift
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Toward single-molecular imaging
• Information of the positions of the individual nuclei → Accurate measurement of e–n int. const’s (A∥, A⊥) ≈ (r, θ) → Lack of information on the azimuthal angle ϕ
• Spectral resolution → Easy to resolve isotopes → Need to measure J-couplings & chemical shifts (ppm!) → Limited by sensor/memory lifetimes (T2e/n, T1e/n)
Nuclear spin
NV spin
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How to determine ϕ?
𝑃Y =12−
12
cos 𝜙 − 𝜙n sin𝑁𝜙cp
Transition probability of the NV spin after the detection of a single nuclear spin
Phys. Rev. B 98, 121405 (2018) Sasaki et al.
Azimuthal angle of the nuclear Bloch vector: 2𝜋𝑓p𝑡 + 𝜙n(0)
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Ensemble vs. single
RF pulse
RF pulse
The initial state matters → Dynamic nuclear polarization (DNP)
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Determination of ϕ of a 13C n-spin
1. DNP (PulsePol) 2. RF pulse@ms = −1 3. Wait t (n-spin precesses) 4. AC sensing
f1 = 215.6 kHz (ms = −1) f0 = fc (ms = 0)
Phys. Rev. B 98, 121405 (2018) Sasaki et al.
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PulsePol
• DNP condition: 2τpol = k/fn (k: odd, fn: nuclear Larmor frequency) • Average Hamiltonian ∝ 𝑆+𝐼− + 𝑆−𝐼+,∝ 𝑆+𝐼+ + 𝑆−𝐼−
Hamiltonian engineering
[PulsePol] Sci. Adv. 4, eaat8978 (2018) Schwartz et al.
Phys. Rev. B 98, 121405 (2018) Sasaki et al.
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PulsePol
fc ft
fc/3 fc/5 ft/3 ft/5
Phys. Rev. B 98, 121405 (2018) Sasaki et al.
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PulsePol
fc ft
fc/3 fc/5 ft/3 ft/5
Phys. Rev. B 98, 121405 (2018) Sasaki et al.
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Determination of ϕ of a 13C n-spin
1. DNP (PulsePol) 2. RF pulse@ms = −1 3. Wait t (n-spin precesses) 4. AC sensing
Phys. Rev. B 98, 121405 (2018) Sasaki et al.
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Determination of ϕ of a 13C n-spin
t → 1 ms (undersampling) fp = 215.79 kHz ≈ f1 = 215.6 kHz ϕ − ϕn(0) = 334.0o ϕn(0) = 89.2o (Real-space n-spin trajectory)
Phys. Rev. B 98, 121405 (2018) Sasaki et al.
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ϕn(0): Real-space n-spin trajectory ϕrf = 0o
Direction of the RF field
Bloch vector@t = 0 (Considering the rotation axis of the n-spin & detuning)
Full simulation based on the Bloch equation (Tilt of q-axis, pulse delay...)
Phys. Rev. B 98, 121405 (2018) Sasaki et al.
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Determination of ϕ of a 13C n-spin
t → 1 ms (undersampling) fp = 215.79 kHz ≈ f1 = 215.6 kHz ϕ − ϕn(0) = 334.0o ϕn(0) = 89.2o (Real-space n-spin trajectory) → ϕ = 247.8±4.1o
Phys. Rev. B 98, 121405 (2018) Sasaki et al.
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Observation of weakly coupled 13C n-spins Ultrahigh resolution sensing (N = 2)
Phys. Rev. B 98, 121405 (2018) Sasaki et al.
• fc = 387.5 kHz • RF pulse@ms = 0 • N = 2 to minimize
back actions from NV
fc ft
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Observation of weakly coupled 13C n-spins Ultrahigh resolution sensing (N = 2)
Phys. Rev. B 98, 121405 (2018) Sasaki et al.
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Summary • Tools for single-molecule imaging/structural analysis
are being developed
→ Determination of the position of a single n-spin[1,2]
→ Ultrahigh resolution sensing on single n-spins[1,3,4]
[1] Phys. Rev. B 98, 121405 (2018) Sasaki, Itoh & Abe (arXiv.1806.00177) [2] Phys. Rev. Lett. 121, 170801 (2018) Zopes et al. (arXiv.1807.04559) [3] Nature Commun. 10, 594 (2019) Pfender et al. (arXiv.1806.02181) [4] Nature 571, 230 (2019) Cujia et al. (arXiv.1806.08243)
→ Suppressing back actions by weak measurement
• Other issues: Create high-quality “shallow” NVs, accurately position single molecules/proteins near the sensor etc