Chalmers University of Technology Quantum acoustics and An atom in front of a mirror Placing artificial atoms in unusual environments Ø Interaction between SAW and a qubit Ø Nonlinear reflection Ø Listening to a qubit relaxing Ø Two tone spectroscopy M.V. Gustafsson et al., Science 346, 207 (2014) Ø An atom in front of a mirror T. Aref et al., arXiv:1506.01631 (2015) Ø Reflecting light from an “atom” Ø Placing an “atom” in front of a mirror Ø Cancelling vacuum fluctuations Ø Summary
I.-C. Hoi et al., Nature Physics 11, 1045 (2015) Per Delsing Quantum Device Physics Chalmers University of Technology Generating and detecting SAW with an IDT
• Piezoelectric substrate (GaAs, quartz, LiNbO3…) • Propagation speed: v ≈ 3000 m/s
• Generator and receiver: The Interdigital Transducer (IDT)
Datta, Surface Acoustic Wave devices, 1986 Morgan, Surface acoustic wave filters, 2007 Per Delsing Quantum Device Physics Chalmers University of Technology Scattering phonons on a qubit Making a transmon into an IDT would allow the qubit to pick up the SAW ≈
We should see the same non-linear behavior as with photons
Sender IDT Transmon Qubit
Per Delsing Quantum Device Physics Chalmers University of Technology Interfacing SAW waves with a qubit
GaAs Aluminum Gold
We have three different controls SAW wave, Gate signal, Flux tuning
Read-out of the acoustic signal
T = 20 mK, f=4.8 GHz
Per Delsing Quantum Device Physics Chalmers University of Technology The Inter Digital Transducer (IDT)
Aluminum on GaAs
IDT width = 25 µm
NIDT = 125
Finger spacing=λ/2=300 nm v=2900 m/s
=> 4.8066 GHz
Morgan, Surface acoustic wave filters, (2007) Datta, Surface Acoustic Wave devices, (1986) Per Delsing Quantum Device Physics Chalmers University of Technology Scattering matrix for the IDT
Scattering matrix for the IDT Only 4 independent matrix elements
1 S11 S21 S21 S = S S S 0 21 22 32 1 S21=S12 S21 S32 S22 @ A S11 With the qubit detuned we see only
the reflection from the IDT => S11 S S33 22 3 f = 4.8066 GHz 2 IDT S11= 0.50
Per Delsing Quantum Device Physics Chalmers University of Technology
The SAW transmon
• With the capacitance C shaped into a finger structure, the qubit couples to SAW! • The coupling rate can be estimated to be
Γ 2 ≈ 0.45 N ⋅ K ⋅ f ≈ 30 MHz 2π Qubit ∆x • N=20 ∆x+λ/2 The number of finger pairs Mechanical • K2=0.07% reflections The electromechanical coupling cancel ! SQUID coefficient for GaAs
Per Delsing Quantum Device Physics Chalmers University of Technology Three types of measurements
Reflection Listening Two-tone spectroscopy
Acoustic in Electric in Electric + Acoustic in Acoustic out Acoustic out Acoustic out
Per Delsing Quantum Device Physics Chalmers University of Technology Reflecting a signal off the IDT 6 5 4 3 2 f [GHz] 1 0 -1.0 -0.5 0.0 0.5 1.0 R [dB]
2 S21 R = S11 i ! i2✓L S22 + 1 e Only electric In the fit we have neglected⇣ pure⌘ dephasing reflection Electric and acoustic reflection Reflection vs. flux
Per Delsing Quantum Device Physics Chalmers University of Technology Acoustic reflection on the qubit
38 (R-S11)peak peak ) 11 11 R-S (R-S
Per Delsing Quantum Device Physics Chalmers University of Technology
Listening to the phonon relaxation
Experiment, listening and pumping at 4.8066 GHz Sweeping the flux and the control amplitude
-95 |3> -100 f 12 f02/2 -105 f02/2 f01 -110 3-photon -115 2-photon -120 Gate Power ( dBm ) -125 1-photon Colors represent phonon signal coming out from -0.3 -0.2 -0.1 0 0.1 0.2 0.3 the IDT Qubit detuning (GHz)
Per Delsing Quantum Device Physics Chalmers University of Technology
Comparing to theory Listening at 4.8066 GHz Experiment Theory
-95 -95
-100 -100 -105 -105 -110 -110 -115 -115 -120 -120 Gate Power (dBm) Gate Power (dBm) -125 -125
-0.3 -0.2 -0.1 0 0.1 0.2 0.3 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 Qubit detuning (GHz) Qubit detuning (GHz)
Fit with Γ = 38 MHz and no pure dephasing Per Delsing Quantum Device Physics Chalmers University of Technology Two-tone spectroscopy Reflection coefficient vs. flux and control frequency – f 01 Exciting f01 and listening to f02 – f12 f12=4.8 GHz Exciting f01 and listening to f01
f01=5.02 GHz
f01=4.8 GHz
Exciting f12 listening to f01
f12=4.58 GHz
Anharmonicity ≈ 220 MHz Per Delsing Quantum Device Physics Chalmers University of Technology Two-tone spectroscopy for different power comparing experiment and theory
Experiment
Theory Theory including 6 qubit levels
Per Delsing Quantum Device Physics Chalmers University of Technology Summary I • Nonlinear reflection of phonons from a transmon qubit. • Listening to emitted phonons • Two tone spectroscopy • Pulsed measurements show the acoustic character M.V. Gustafsson et al., Nature Physics, 8, 338 (2012) M.V. Gustafsson et al., Science 346, 207 (2014) A. Frisk-Kockum et al., Phys. Rev. A, 90, 013837 (2014) T. Aref et al., arXiv:1506.01631 (2015)
Experiment Theory
Martin Thomas Maria Göran Anton Gustafsson Aref Ekström Johansson Frisk-Kockum
Per Delsing Quantum Device Physics Chalmers University of Technology Placing an atom in front of a mirror
We place an “atom” (or superconducting qubit) on a chip We limit the electromagnetic field to one dimension
A mirror is made by a thin metallic layer that shorts the electric field. We use a superconducting short in 1D as a mirror.
Per Delsing Quantum Device Physics Chalmers University of Technology A) B) ωp 1 2 Transmission for a single “atom” (no mirror) VR VT RT Microwaves are sent on resonance Nonlinear V transmission in LPF Amplifier -20dB towards the qubit and transmission is At low power everything is reflected by the qubit -20dB 4K measured 320320 umum At high power everything is transmitted -10dB DC Block -10dB 1K 10um
-30dB BPF -30dB C) 1 R T 30mK 0 T
Cc
100nm100nm “Atom” P
Total extinction: 99.6% extinction observed
Shen and Fan, PRL (2005). Astafiev et al. Science (2010) Hoi et al. PRL (2011) Per Delsing Quantum Device Physics Chalmers University of Technology Placing an atom in front of a mirror
Atom-mirror distance L=11 mm Sample layout Mode structure for L=λ/2 and L=3λ/4
We can change the atom frequency, thus effectively changing the distance to the mirror, i.e. the distance measured in number of wavelengths.
Per Delsing Quantum Device Physics Chalmers University of Technology Measurement set-up
The atom is placed at the distance L= 11 mm from the mirror.
We measure microwave reflection from the atom/mirror system
Per Delsing Quantum Device Physics Chalmers University of Technology Doing spectroscopy on the “atom”
Reflection at low power
From the dip we can extract
the relaxation rate Γ1 and decoherence rate γ
Per Delsing Quantum Device Physics Chalmers University of Technology Reflection from the atom and the mirror Nonlinear reflection of microwaves off the ”atom” On resonance At low power the microwaves are reflected from the atom. At high power the microwaves are reflected by the mirror
Control experiment for relaxation rate Γ1 and decoherence rate γ
Per Delsing Quantum Device Physics Chalmers University of Technology Doing spectroscopy on the “atom” Spectroscopy Extracting the relaxation rate The ”atom” is invisible around 5.4 GHz
The quantum fluctuation from the transmission line and from the mirror interfere T1 differs by a factor of 10
Per Delsing Quantum Device Physics Chalmers University of Technology Measuring the quantum fluctuations
Quantum fluctuations are hard to measure since you cannot extract the energy.
Spontaneous emission of an atom is caused by quantum fluctuations, so measuring the decay rate, we can indirectly measure the quantum fluctuations.
The quantum fluctuation from the transmission line and from the mirror interfere
Per Delsing Quantum Device Physics Chalmers University of Technology Measuring the vacuum fluctuations as a function of the distance to the mirror Narrow range Wider range
When the ”atom” is half a wavelength from Probe power corresponds to 0.04 photons the mirror the quantum fluctuations vanish (only for the atom-frequency) I.-C. Hoi et al., Nature Physics 2015 Per Delsing Quantum Device Physics Chalmers University of Technology Summary II • Investigated an atom in front of a mirror • The life time of an atom can be modified in front of a mirror • Quantum fluctuations can be canceled to extend the life time of atoms
I.-C. Hoi et al., Nature Physics 11, 1045, (2015) Experiment Theory
IoChun Chris Arsalan Göran Lars Anton Hoi Wilson Pourkabirian Johansson Tornberg Frisk-Kockum Per Delsing Quantum Device Physics