1. Per Delsing Chalmers University of Technology Quantum Device Physics Interaction between artificial atoms and microwaves Experiments: IoChun Hoi, Chris Wilson, Tauno Palomaki Theory collaboration: Anton Frisk-Kockum, Borja Peropadre, Göran Johansson  Introduction  Artificial atoms  Microwave reflection from a single atom  The photon router  Nonclassical microwaves  Atom in front of a mirror

2. Per Delsing Chalmers University of Technology Quantum Device Physics LT28 conference9 – 16 August 2017 Abstract submission10 Apri l2017 Early-bird registration 1 May 2017 Paper submission15 June 2017 Subtopics 1.Quantum fluids and solids 2.Superconductivity 3.Cryogenic techniques and applications 4.Magnetism and quantum phase transitions 5.Quantum transport and quantum information in condensed matter Invited speakers, prizes Oral and poster presentations Peer-reviewed proceedings in J. Phys. Conf. Series Exhibitions Excursion, banquet www.LT28.se

3. Per Delsing Chalmers University of Technology Quantum Device Physics Photons interacting with an artificial atom V 1+ V 1- V 2_ 10 um Qubit in a transmission line, interaction with microwave photons Strong coupling 1D-modes Large dipole moment ~5 GHz ~20-50 mK

4. Per Delsing Chalmers University of Technology Quantum Device Physics Introduction An artificial atom Microwave reflection from a single atom The photon router Nonclassical microwaves Atom in front of a mirror Outline

5. Per Delsing Chalmers University of Technology Quantum Device Physics Artificial atoms based on Josephson junctions Quantized electrical circuit Harmonic oscillator is not an atom Nonlinearity makes the circuit anharmonic and addressable Small JJ is a good nonlinear inductor

6. Per Delsing Chalmers University of Technology Quantum Device Physics The transmon qubit as an artificial atom Jens Koch et. al. PRA (2007) E 01 /h A capacitively shunted Cooper-pair box

7. Per Delsing Chalmers University of Technology Quantum Device Physics Introduction An artificial atom Microwave reflection from a single atom The photon router Nonclassical microwaves Atom in front of a mirror Outline

8. Per Delsing Chalmers University of Technology Quantum Device Physics Transmission and Reflection Similar experiments by Astafiev, et al., NEC Science (2010). On resonance, low power Reflection coefficientTransmission coefficient

9. Per Delsing Chalmers University of Technology Quantum Device Physics Reflection and exctinction Constructive interference for the reflected wave Destructive interference for the transmitted wave Total extinction

10. Per Delsing Chalmers University of Technology Quantum Device Physics Measurement set-up Measuring both transmission and reflection simultaneously System noise temperature ~6K

11. Per Delsing Chalmers University of Technology Quantum Device Physics Transmission measurement Almost full reflection at low power Almost full transmission at high power

12. Per Delsing Chalmers University of Technology Quantum Device Physics Transmission measurement MagnitudePhase   1 /2π = 73MHz,   2 /2π = 55MHz,  01 /2π = 7.1GHz   /2π 18MHz

13. Per Delsing Chalmers University of Technology Quantum Device Physics Two-Tone Spectroscopy f probe Pumping the 0-1 transition varying power probing transmission at low power varying f |2> |1> |0> f 01

14. Per Delsing Chalmers University of Technology Quantum Device Physics Autler Townes splitting f c =f 12 f probe Rabi dressed states Pumping the 1-2 transition, varying power probing the 0-1 transition varying f Autler Townes splitting, when Ω>  01 Allows calibration of power at the sample

15. Per Delsing Chalmers University of Technology Quantum Device Physics Introduction An artificial atom Micrrowave reflection from a single atom The photon router Nonclassical microwaves Atom in front of a mirror Outline

16. Per Delsing Chalmers University of Technology Quantum Device Physics Single Photon Router A single photon gets reflected if no control pulse is sent When a control pulse is sent the first level is Rabi dressed and the photon is transmitted Control pulse Transmon qubit Output 1Output 2 Signal in I.-C. Hoi et al. Physical Review Letters, 107, 073601 (2011)

17. Per Delsing Chalmers University of Technology Quantum Device Physics The On-Off ratio Rerouting a single photon with a fast pulse f 12 f 01 Rabi dressed states Sample 1 Sample 2

18. Per Delsing Chalmers University of Technology Quantum Device Physics How fast is the router Transmission for different pulse times: 50ns to 1µs Routing photons on the 10 ns scale, Limited by 1/   1  2ns Strong coupling is good, this improves both speed and on/off ratio 10 ns pulse times

19. Per Delsing Chalmers University of Technology Quantum Device Physics Control pulse Cascading routers to a multiplexer Output 1 Signal in Output 2Output 3 Output 4 Different anharmonicity for the different qubits

20. Per Delsing Chalmers University of Technology Quantum Device Physics Introduction An artificial atom Microwave reflection from a single atom The photon router Nonclassical microwaves Atom in front of a mirror Outline

21. Per Delsing Chalmers University of Technology Quantum Device Physics Measuring the 2 nd order correlation function For optical frequencies there are single photon detectors Bozyigit, et al. Nature Physics, 7, 154 (2011)

22. Per Delsing Chalmers University of Technology Quantum Device Physics Comparing different sources

23. Per Delsing Chalmers University of Technology Quantum Device Physics Photon Number Filter

24. Per Delsing Chalmers University of Technology Quantum Device Physics Measuring correlations

25. Per Delsing Chalmers University of Technology Quantum Device Physics Testing the set-up, thermal versus coherent No free fitting parameters

26. Per Delsing Chalmers University of Technology Quantum Device Physics Measuring the transmitted field, bunching

27. Per Delsing Chalmers University of Technology Quantum Device Physics The reflected field, anti bunching g (2) (  ) for two different powers Non-idealities: Trigger jitter, T≠0, Circulator not perfect… Hoi et al. New J. Phys. (2012) Peropadre et al. New J. Phys. (2012) Theory

28. Per Delsing Chalmers University of Technology Quantum Device Physics Introduction An artificial atom Microwave reflection from a single atom The photon router Nonclassical microwaves Atom in front of a mirror Outline

29. Per Delsing Chalmers University of Technology Quantum Device Physics 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.

30. Per Delsing Chalmers University of Technology Quantum Device Physics Placing an atom in front of a mirror We can change the atom frequency, thus effectively changing the distance to the mirror, i.e. the distance measured in number of wavelengths. Sample layoutMode structure for L= /2 and L=3 /4 Atom-mirror distance L=11 mm

31. Per Delsing Chalmers University of Technology Quantum Device Physics 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

32. Per Delsing Chalmers University of Technology Quantum Device Physics Doing spectroscopy on the “atom” Reflection at low power From the dip we can extract the relaxation rate  1 and decoherence rate 

33. Per Delsing Chalmers University of Technology Quantum Device Physics Reflection from the atom and the mirror Nonlinear reflection of microwaves off the ”atom” 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  1 and decoherence rate  On resonance Reflection: Magnitude and phaseReflection: Real and Imaginary Atom reflection Mirror reflection

34. Per Delsing Chalmers University of Technology Quantum Device Physics Doing spectroscopy on the “atom” Spectroscopy The ”atom” is invisible around 5.4 GHz Extracting the relaxation rate The quantum fluctuation from the transmission line and from the mirror interfere T 1 differs by a factor of 10

35. Per Delsing Chalmers University of Technology Quantum Device Physics 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

36. Per Delsing Chalmers University of Technology Quantum Device Physics 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 the mirror the quantum fluctuations vanish (only for the atom-frequency) Probe power corresponds to 0.04 photons I.-C. Hoi et al., Nature Physics 11, 1045, (2015)

37. Per Delsing Chalmers University of Technology Quantum Device Physics Summary Nonlinear reflection on an artificial atom Demonstration of a Photon router with 99% on-off ratio Nonclassical states Probing and canceling vacuum fluctuations Chris Wilson Göran Johansson IoChun Hoi Tauno Palomaki Borja Peropadre Hoi et al. Physical Review Letters, 107, 073601 (2011) Hoi et al. Physical Review Letters, 108, 263601 (2012) Hoi et al. Nature Physics, 11, 1045 (2015) Anton Frisk-Kockum