Magnon-polaritons from room
temperature down to milliKelvin
temperature
Martin P. WeidesJohannes Gutenberg University Mainz, Germany
and Karlsruhe Institute of Technology (KIT), Germany
Interface magnons with
superconducting quantum circuits
Martin Weides KIT & JGU Mainz 2
� Introduction
� QuantumMagnonics
� Superconducting quantum circuits
� Multi-level spectroscopy, magnetic dipole qubit,
high coherence
� Magnonics
� Classical to quantum
Martin Weides KIT & JGU Mainz 3
Magnon: quantized spin wave excitation
Future information technology
(e.g. spin-torque oscillator, spin-wave propagation control for logic)
Strong magnon damping: magnon/phonon/electron scattering
Grand challenge:
To understand physics, single magnon information needed!
Slavin et al., Nat. Nanotech. ´09 Vogt et al., Nat. Commun. ´14
Attenuation length ~10 umLinewidth Δf > 1 MHz
Magnonics: spin waves in nanostructures
Martin Weides KIT & JGU Mainz 4
‘Classical measurement’:
� Inelastic scattering (neutron, photon, electron)
� Ferromagnetic resonance
Drawbacks:
� Weakly (not coherent) coupled
� Large flux, small signal (statistics)
� Thermally excited population (T > 4 K)
Difficult to access magnon ground state!
Status quo
magnonscattered
incident
Martin Weides KIT & JGU Mainz 5
� Quantum ground state (T=10 mK)
� Ultra-low power spectroscopy, coherent coupling
� How to achieve?
Extend magnon to artificial spin!
Access magnon lifetime and coherence via coherent coupling
How to probe a single magnon?
Martin Weides KIT & JGU Mainz 6
Strong coupling:
� Qubit < 1 MHz
� Magnon Ni80Fe20 < 50 MHz, Y3Fe5O12< 5 MHz
Coupling rate g (N number of spins in qubit mode volume V0)
> 10 MHz (strong coupling)
Coherent coupling requirement
Martin Weides KIT & JGU Mainz 7
� Introduction
� QuantumMagnonics
� Superconducting quantum circuits
� Multi-level spectroscopy, magnetic dipole qubit,
high coherence
� Magnonics
� Classical to quantum
Martin Weides KIT & JGU Mainz 8
Transmons: capacitively shunted Josephson junction
� Anharmonic oscillator
Non-linear, tunable LC oscillator
Magnetic flux Φ changes LJ(φ)
Φ
Two lowest levels � Bloch sphere
Martin Weides KIT & JGU Mainz 9
KIT quantum lab
�Al, Nb, NbN films
�Al-AlOx-Al tunnel junctions (shadow evaporated)
� Lithography, etching (Nanostructure Service Laboratory)
�He3/He4 dilution fridge (40cm base plate)
�18 RF & 24 DC lines, filters, 5 amps
�9 quantum chips
� Spectroscopy, time-domain setups
� Software (simulation, measurement)
�QKIT on GitHub
200 nm
Martin Weides KIT & JGU Mainz 11
Anharmonic many-level quantum circuit
Consider higher quantum levels
transmon qubit:
weak anharmonicity
Neeley Nat. Phys. 4 (2008)
Fedorov Nat. 481 (2011)
Bruß PRL 88 (2002)
Cerf PRL 88 (2002)
Paraoanu JLTP 175 (2014)
enhanced security of key
distribution in quantum
cryptography
quantum
simulation
spin-½ ↔ two levels
spin-1 ↔ three levels
efficient & robust
quantum gates
Martin Weides KIT & JGU Mainz 12
Qubit sample
� microstrip geometry
� overlap Josephson junction
� transmon regime: �� ≫ �� ⇒ ��~0.05
� spectroscopic measurements
� VNA readout tone
� microwave drive/probe tone
TL
Blais PRA 69 (2004)
Koch PRA 76 (2007)
Sandberg APL 102 (2013)
Martin Weides KIT & JGU Mainz 13
High power spectroscopy
exc
ita
tio
nto
ne
(G
Hz)
dis
pe
rsiv
e r
eso
na
tor
shif
t
���/2�
1
2���/2�
1
3���/2�
1
4���/2�
Multi-photon transitions
�determine qubit parameter EJ, E
C
Koch et al. PRA 2007
Braumüller et al., PRB 2015
Martin Weides KIT & JGU Mainz 14
Multiphoton dressing – pumping the |��-level
Dynamical coupling of levels by probe tone �
Autler-Townes doublet like avoided crossing
measurement
simulation
Braumüller et al., PRB 2015
Sweep drive & probe freqs.
Martin Weides KIT & JGU Mainz 15
Transmon qubit – Concentrically shaped electrodes
pad geometry
� dipole antenna
Sandberg, MW, APL 102 (2013)
concentric geometry
� reduced radiation/crosstalk
Koch, PRA 76 (2007)
� �� � 4�� �� ��� �� cos �
� Operation in phase regime, �� ≫ ��
Martin Weides KIT & JGU Mainz 16
Geometry of concentric, gradiometric transmon
� Central island and concentric ring electrode,
interconnected by two Josephson junctions, �� ��⁄ ~120
� Gradiometric dc-SQUID loop � fast frequency control
� Dispersive qubit readout
Martin Weides KIT & JGU Mainz 17
Main features
� Hybrid coplanar/microstrip design
� Minimize defect loss at surface and interface oxides
� Straightforward fabrication:
� Optical lift-off lithography
� Electron beam lithography, shadow-angle evaporation
Martin Weides KIT & JGU Mainz 19
Dissipative dynamics – Loss contributions
Purcell
Γ�� � 16μs
Dielectric defects
Γ�� � 26μsRadiation
Γ�� � 100μs
⇒Γ�� � 9μs
Martin Weides KIT & JGU Mainz 21
Pulsed measurements – fast control of qubit frequency
Braumüller et al., APL (2016)
Martin Weides KIT & JGU Mainz 22
Fast qubit tuning � Full tomographic control
SSB-mixing, shaped pulses (DRAG)
�Gate benchmarking (99.54%)
Measured
Expected
x
y
z
Martin Weides KIT & JGU Mainz 23
Consider geometric loop inductance
� Good agreement for �� � 0.6nH
Artificial spin array with non-trivial
couplings
� (analog) spin system simulation
Reiner, Marthaler, Braumüller, MW, et al.
arXiv 1602.05600 (2016)
Martin Weides KIT & JGU Mainz 24
Quantum SWAP (Qubit-Resonator)
1. Excite qubit off-resonance to resonator
2. Bring on-resonance and hold for ∆t
3. Detune qubit and readout
� Quantum-Setup works! DC & RF electronics, pulse shaping, bias tee, software…
� Controlled quantum SWAPs (qubit-HO)
P0
P1
Martin Weides KIT & JGU Mainz 25
� Introduction
� QuantumMagnonics
� Superconducting quantum circuits
� Multi-level spectroscopy, magnetic dipole qubit,
high coherence
� Magnonics
� Classical to quantum
Martin Weides KIT & JGU Mainz 26
Yttrium iron garnet (Y3Fe
5O
12)
� Electrically insulating ferrimagnet
� Empty 4s, half filled 3d orbitals � no orbital momentum, s=5/2
� Five Fe3+ ions per unit cell form sublattices of opposing
magnetization � approximated as ferromagnet
� Extremely low spin-wave damping
spin wave decay length on the order of centimeters
� TCurie = 559K
� High spin density ρ= 4.22∙1027 1/m3
� Anisotropic, [110]-axis is soft magnetic
Martin Weides KIT & JGU Mainz 27
Magnons
Precessional motion of magnetization M, Landau–Lifshitz eq.
k=0 � precessing macrospin with Kittel resonance frequency
Quasiparticles, collective excitation of the electrons' spin structure
in crystal lattice
Outer magnetic field H removes degeneracy
Martin Weides KIT & JGU Mainz 28
Spin waves affect static and dynamic magnetization
Spin wave: spin-lattice excitation in magnetically ordered material
Harmonic variation (wavelength �) in phase of precession of adjacent spins
about the local magnetization direction (parallel to magnetic field �)
Single magnon= � flip (i.e. 180° rotation) of a single spin
Saturation magnetization �S
Change in static magnetization: Δ�Z= �
S(1 − cos �)
� notional precessional angle of spins about magnetization direction
AC magnetization perturbation (vector rotating at magnon frequency �)
Δ�AC
= �Ssin � in-plane perpendicular to Δ�
Z.
For small �:
� Reduction in static magnetization Δ�Z≃�
S�2/2
� Increase in dynamic magnetization Δ�AC
= �S�
Martin Weides KIT & JGU Mainz 29
Magnon-Cavity experiments (incomplete…)
Since 2014 rapid growth of publications
� Tabuchi et al. PRL 2014Hybridizing Ferromagnetic Magnons and Microwave Photons in the Quantum Limit
� Zhang et al. PRL 2014Strongly Coupled Magnons and Cavity Microwave Photons
� Goryachev et al. PR Applied 2014High-Cooperativity Cavity QED with Magnons at Microwave Frequencies
� Cao et al. PRB 2015Exchange magnon-polaritons in microwave cavities
� Zhang et al. NPJ 2015Cavity quantum electrodynamics with ferromagnetic magnons in a small yttrium-iron-garnet sphere
� Tabuchi et al. Science 2015Coherent coupling between a ferromagnetic magnon and a superconducting qubit
� Bourhill et al. arXiv 2016Ultra-High Cooperativity Interactions between Magnons and Resonant Photons in a YIG sphere
Martin Weides KIT & JGU Mainz 30
3d cavity resonator
Marcel Langer BA thesis KIT (2015)
Magnetic field distribution
1st mode 2nd mode
YIG sphere
Martin Weides KIT & JGU Mainz 31
3d cavity-Kittel mode (YIG) � strong coupling
� Few/ single magnon excitations (mK)
� Linewidth and noise
� Extend to qubit
� 4 to 300 K
� Up to Tesla-fields
� Extend to thin films
Two setups
(classical and quantum)
Martin Weides KIT & JGU Mainz 32
Temperature dependence down to 5K
Reducing temperature
� Coupling strength g increases
� Resonant magnetic field decreases
� Additional modes appear & disappear
cf. Zhang et al. NPJ 2015
Reentrant cavity,
see Goryachev et al.
PR Applied 2014
Martin Weides KIT & JGU Mainz 33
Approaching quantum: magnon-polaritons at 500mK
κin = 65 kHz
κm = 2.4 MHz
κr = 0.9 MHz
g= 27.8 MHz
Extraction from fit
Non-uniform modes visible
Martin Weides KIT & JGU Mainz 34
Coupling qubit to magnon
+ qubit readout resonator (not shown)
Straightforward:
coupling via 3d cavity (modes for coupling, Q-readout)
Tabuchi et al., Science 2015
Martin Weides KIT & JGU Mainz 35
Transmon qubit coupled to 3d cavity
Grünhaupt MA thesis (2016)
3d cavity: quantized field suppresses radiative loss
low E-fields and weak coupling to surface TLSs
� Long coherence T1 ≈15 µs, T2 ≈ 16 µs, T2* ≈ 30 µs
Martin Weides KIT & JGU Mainz 36
Hybrid quantum systems
Dry 10mK fridge (July `16)�Magnon-polaritons from RT � 0.5K
�YIG sphere and thin films
�Spectroscopy and pulsed measurement setup ready
Martin Weides KIT & JGU Mainz 37
QKIT framework - an extension to qtlab written in python
Open-source measurement software QKIT https://github.com/qkitgroup/qkit
• Collection of ipython notebooks for measurement and data analysis
• hdf5 based data storage of 1,2 and 3d data
• 1 and 2d data viewer
• Extended and maintained drivers for low and high frequency electronics
• Large parts of the framework can be used independently of qtlab
• Classes for data fitting, e.g. of microwave resonator data. This includes also a
robust circle fit algorithm (Probst et al. Rev. Sci. Instrum. 86, 024706 (2015))
Martin Weides KIT & JGU Mainz 38
Team
BA
Oliver Hahn
Moritz Kappeler
Tomislav Piskor
MA
Julius Krause
Lukas Grünhaupt
Yannick Schön
Patrick Winkel
Max Zanner
PhD
Jochen Braumüller
Marco Pfirrmann
Steffen Schlör
Andre Schneider
Ping Yang
Technician
Lucas Radtke
Scientists
Hannes Rotzinger
Sasha Lukashenko
Alexey Ustinov
@JGU Mainz
Isabelle Boventer
Mathias Kläui
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