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F. Della Valle Dipartimento di Fisica , Università di Trieste, and INFN Sez . di Trieste on behalf of the MIR collabo

The MIR * experiment: towards an in-vacuum detection of the Dynamical Casimir Effect. F. Della Valle Dipartimento di Fisica , Università di Trieste, and INFN Sez . di Trieste on behalf of the MIR collaboration G. Galeazzi , G. Ruoso (LNL – PADOVA)

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F. Della Valle Dipartimento di Fisica , Università di Trieste, and INFN Sez . di Trieste on behalf of the MIR collabo

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  1. The MIR* experiment: towards an in-vacuum detection of the Dynamical Casimir Effect F. Della Valle Dipartimento di Fisica, Università di Trieste, and INFN Sez. di Trieste on behalf of the MIR collaboration G. Galeazzi, G. Ruoso (LNL – PADOVA) C. Braggio, G. Carugno (PADOVA) A. Agnesi, F. Pirzio, G. Reali (PAVIA) F. Massa, D. Zanello (ROMA) F. Della Valle, G. Messineo (TRIESTE) * Motion Induced Radiation F. Della Valle - QFEXT 2011 - Benasque, 18-24 September 2011

  2. Outline • Dynamical Casimir Effect • Introduction to the MIR experimental scheme • Optimization of the experimental parameters to maximize the gain • Parametric excitation of a pre-charged field in the cavity • Preliminary data analysis and discussion • Perspectives and Conclusions F. Della Valle - QFEXT 2011 - Benasque, 18-24 September 2011

  3. Dynamical Casimir effect Motion Induced Radiation from a Vibrating Cavity Lambrecht, Jaeckel, and Reynaud 1996, Phys. Rev. Lett.77, 615 ‹Nph› ~ m T 2 Due to dissipative effects against the quantum vacuum, non-uniformly accelerated boundaries should emit real photons with energies corresponding to the Fourier frequencies of the movement. “Generation of particles pairs out of vacuum fluctuations via quantum squeezing induced by time-dependence of macroscopic boundary conditions” Quantum theory of electromagnetic field in a variable-length one-dimensional cavity Moore 1970, J. Math. Phys. 11, 2679 Radiation from a moving mirror in two dimensional space-time: conformal anomaly Fullingand Davies 1976, Proc. R. Soc. Lond. A 348, 393 Oscillating mirror m/2p~ 10 GHz T ~ 1 s observation time  =v/c= 10-7 ‹Nph› << 1 effectisnotdetectable Resonating Cavities to increase the signal F. Della Valle - QFEXT 2011 - Benasque, 18-24 September 2011

  4. MIR experimental scheme - 1 • MAIN INGREDIENTS • Modulation of the surface conductivity of a semiconductor slab • Parametric amplification inside a microwave cavity (frep = 2f0) • A novel experimental approach for the detection of the dynamical Casimir effect • Braggioet al. 2005, Europhys. Lett. 70, 754 Accelerating reference frame for electromagnetic waves in a rapidly growing plasma: Unruh-Davies-De Witt radiation and the nonadiabaticCasimir effect E. Yablonovitch 1989, Phys. Rev. Lett.62, 1742 Parametric excitation of vacuum by use of femtosecond pulses Lozovik, Tsvetus, and Vinogradov 1995, PhysicaScripta52, 184 Quantum phenomena in nonstationary media Dodonov, Klimov, and Nikonov 1993, Phys. Rev. A47, 4422 F. Della Valle - QFEXT 2011 - Benasque, 18-24 September 2011

  5. MIR experimental scheme - 2 • Requirements: • RF cavity geometry: high stationary frequency shift, small illumination area, f0≈ 2.5 GHz,Q0≈ 104–106 • laser system: high frequency repetition rate (frep≈5 GHz, stability better than the cavity BW 1 kHz),tunable frep, ~10 pspulse duration, Epulse fewmicrojoule, 780 – 820 nm output wavelength • semiconductor:d ≈ 1 mm thickness, high mobility (1 m2/V s @ 4 K), recombination time of a few picoseconds • low noise microwave receiver: sensitivity a few hundreds of 10-5 eV energy photons (i.e. 10-22W/Hz) • Braggioet al. 2009, NIM A 603, 451 F. Della Valle - QFEXT 2011 - Benasque, 18-24 September 2011

  6. Theory V. V. Dodonov Calculations with realistic MIR experimental conditions Results: a significant amount of Dynamical Casimir photons (>103) can be produced in MIR experiment with feasible parameters Calibration of the apparatus with a pre-charged field or with thermal photons Dynamical Casimir effect at finite temperature Plunien,Schuetzhold, and Soff 2000, Phys. Rev. Lett.84, 1882 simulation F. Della Valle - QFEXT 2011 - Benasque, 18-24 September 2011

  7. MIR experimental scheme - 3 80 lLHe vessel, T = (0.8 ÷ 9) K 30 l F. Della Valle - QFEXT 2011 - Benasque, 18-24 September 2011

  8. Microwave Cavity Cylindrical reentrantcavity (Fcav = 42 mm, h = 34 mm, FGaAs = 8 mm, d = 10 mm) Nb superconducting cavity (80 x 90 x 9) mm3 • Smaller amount of Epulse • Simplified optical scheme for uniform illumination of the semiconductor E, H field profiles E, H field profiles Note that: - @ semiconductor position: E ≈ 0 (rectangular cavity); E = Emax (cylindrical reentrantcavity) - opposite sign of the frequency shift F. Della Valle - QFEXT 2011 - Benasque, 18-24 September 2011

  9. Laser system - 1 Epulse≈ 10 J; since the average power of a CW mode-locked laser having this value of energy per pulse would be too high, we developed a laser delivering a macropulse of ∆T = 350 – 450 nsduration (~ 2000 pulses). Total macropulse energy is a few tens of millijoules FINAL SPECS - high frequency repetition rate (frep≈5 GHz, stability better than the cavity BW 1 kHz), - tunable frep, - 10 ps pulses duration, - Epulse≈ fewmicrojoules, - 780 – 820 nm output wavelength Agnesiet al., Optics Express13, 5302 (2005) Optics Express14, 9244 (2006) Optics Express16, 15811 (2008) F. Della Valle - QFEXT 2011 - Benasque, 18-24 September 2011

  10. Laser system - 2 LASER repetition rate stability and tuning Active control of the Master Oscillator length: the feedback system locks the repetition frequency of the laser to a reference microwave generator SHORT TERM STABILITY LONG TERM STABILITY > < ~1 kHz F. Della Valle - QFEXT 2011 - Benasque, 18-24 September 2011

  11. Laser system - 3 AUTOCORRELATION MEASUREMENT TRAIN OF PULSES Sampling BW 20 GHz Photodiode rise time 50 ps GaAs ILLUMINATION BEAM PROFILE F. Della Valle - QFEXT 2011 - Benasque, 18-24 September 2011

  12. Semiconductor- 1 Requirements: high mobility (1 m2/V s) short recombination time (a few picosecons) R&D on a new material, starting from semi-insulating (SI) GaAs SI GaAs irradiated with thermal neutrons (Italy, USA) SI GaAs irradiated with Au, Br ions (Tandem accel. in LNL) SI GaAs irradiated with 1-5 MeV protons (CN accel. in LNL) Requirements: high mobility (1 m2/V s) short recombination time (a few picosecons) R&D on a new material, starting from semi-insulating (SI) GaAs SI GaAs irradiated with thermal neutrons (Italy, USA) SI GaAs irradiated with Au, Br ions (Tandem accel. in LNL) SI GaAs irradiated with 1-5 MeV protons (CN accel. in LNL) Foulon et al. 2000, J. Appl. Phys.88,3634 Mangeney et al. 2002, Appl. Phys.Lett. 80,4711 Mangeneyet al. 2000, Appl. Phys. Lett.76,40 Measurement of the recombination time and mobility of the irradiated samples Optical-pump terahertz-probe setup in SELITEC Vilnius, Lituania (profKrotkus group) Same concentration of free carriers produced as in the plasma mirror (n≈ 1017cm-3); Measurements are conducted at different temperatures in the range 300 – 10 K in a cryocooler F. Della Valle - QFEXT 2011 - Benasque, 18-24 September 2011

  13. Semiconductor- 2 Measurements of mobility and recombination time with the optical-pump terahertz-probe setup: the terahertz transmission signal is connected to thevariation of the GaAs conductivity 240 MeV Br14+ ions: 20 m thickness of irradiated material Recombination time at different temperatures 1 – 5 MeV protons: 100 m thickness of irradiated material Recombination time ad different irradiation doses ions/cm2 MOBILITY is inferred by comparison between the terahertz transmitted amplitude through the non-irradiated sample and the same sample after the irradiation procedure After irradiation the mobility is 5 – 10% of the initial value (highest at 80 K). Still sufficient! F. Della Valle - QFEXT 2011 - Benasque, 18-24 September 2011

  14. Stationary frequency shift - 1 The total number of produced photons depends exponentially on the frequency shift Lcavity length Results obtained with Ansoft HFSS (stationary boundary conditions, volume plasma) dsemiconductor thickness stationary frequency shift Df (MHz) F. Della Valle - QFEXT 2011 - Benasque, 18-24 September 2011

  15. Stationary frequency shift - 2 stationary frequency shift f = fill – f0 GEOMETRY A GEOMETRY B stationary frequency shift Df (MHz) F. Della Valle - QFEXT 2011 - Benasque, 18-24 September 2011

  16. Stationary frequency shift - 3 Measuring the stationary frequency shift f = fill– f0 • NON-IRRADIATED SEMICONDUCTOR • tfew nanoseconds @ T = 290 K •  100 s@ T = 77 K • The free carrier plasma lasts for the whole duration of the macropulse (t 400 ns). fill = 2327.200  0.044 MHz Qill= 1500  100 f0= 2338.400  0.014 MHz Q0 = 6200  100 f =fill – f0= – 11 MHz fill = 2303.08  0.05 MHz Qill= 2600  100 f0= 2329.50  0.05 MHz Q0 = 8500  100 f =fill – f0= – 26.4 MHz We obtain the samefforeseen by the simulations. In both cases there is a volume plasma F. Della Valle - QFEXT 2011 - Benasque, 18-24 September 2011

  17. Stationary frequency shift - 4 In the previous measurement the free carriers are present in the overall GaAs volume. During the experiment we use instead a short very thin film of photoexcited carriers Thickness of the plasma is determined by absorption of light: I = I0exp(–x) at T = 77 K for  = (810  10) nm, the absorption coefficient is -1 ≈ 1 m Optical absorption of gallium arsenide between 0.6 and 2.75 eV M. D. Sturge 1962, Phys. Rev.127, 768 Measurement with a thin metallic mirror: 1 micron evaporated Cu f0= 2.3285  0.1 MHz Q0 = 5000  100 fCu= 2.3005  0.1 MHz Q0 = 5000  100 f=fCu–f0 ≈ 28 MHz These measurements are not sufficient to characterize the “moving mirror” F. Della Valle - QFEXT 2011 - Benasque, 18-24 September 2011

  18. Parametric excitation of an external field - 1 GAIN OF THE PARAMETRIC AMPLIFIER t = 800 ns The cavity unperturbed modef0is critically coupled to the transmission line; the cavity is pre-charged the radiofrequency at the frequency f0of the unperturbed cavity is switched off and the EM field starts to decay with decay time 0(free oscillations); no laser F. Della Valle - QFEXT 2011 - Benasque, 18-24 September 2011

  19. Parametric excitation of an external field - 2 ~100 nsafterswitching off the externalgenerator, during the fielddecay, the laser trainofpulsesimpinges on the semiconductor surface > < ~400 ns A(laserOFF) A(laserON) GAIN of the parametricamplifier = A(laserON)/A(laserOFF) Amplificationisneverobserved! F. Della Valle - QFEXT 2011 - Benasque, 18-24 September 2011

  20. Experiment simulation: RLC circuit - 1 pulse generator  train of pulses • thiscircuitgenerates a voltage V2 whichisthenusedtomathematicallymodifycapacity C1 • Dtexcexcitationperiod • temporalshapeof the excitation (rise/decaytime - duration) • TD delaylinetochange the phasebetween the excitation and the free oscillations RLC circuit  unperturbed cavity • f0 =1/2(LC)1/2free oscillations frequency • Q0 = R/w0Lqualityfactor of the unperturbedcavity RLC with variable capacitance  parametric excited cavity • coefficient of V2 determines C, corresponding to a frequency shift in the cavity|f| = f C/2C • Qexc = Rparallel/w0L quality factor of the perturbedcavity F. Della Valle - QFEXT 2011 - Benasque, 18-24 September 2011

  21. Experiment simulation: RLC circuit - 2 Transient analysis: evolution of an initial applied voltage level  pre-charged field Example FREE OSCILLATIONS f0= 2516.51 MHz; Q0 = 5000 MODULATION stationary frequency shiftDf = 8.5 MHz 2 ps rise time – 8 ps duration – 2 ps decay time at parametricresonance exponentialgrowthof the fieldamplitude GAIN = ratiobetween the initialvoltage and itsamplitudeafter 400 ns G = 300V/V IC = 1V Time (ns) F. Della Valle - QFEXT 2011 - Benasque, 18-24 September 2011

  22. Experiment simulation: RLC circuit - 3 Dtexc ≈ 200 ps Texc = 198.71 psdf = 0.28 MHz Texc = 198.77 psdf = 1.04 MHz phase delay (ps) df (MHz) exponentialgrowth at the parametricresonance; decayingoscillationswhendetuned higherordermaxima in the gainvs. dfplot are observed the maximum of the amplification is found atfrep=2f0 +df(in our experiment the excitation is not a pure harmonic signal?); If the phasebetween the excitation and the field in the cavityvaries, at each laser shot a differentgainisobserved; In agreement withV.V.Dodonovtheoreticalresults Parametric amplification of the classical field in cavities with photoexcited semiconductors,Phys. Scr. T143, 014009(2011) F. Della Valle - QFEXT 2011 - Benasque, 18-24 September 2011

  23. Parametric excitation of an external field - 3 Isourparametricamplifiercharacterizedby a gainallowing the observationof the vacuumcontribution? To test the apparatus and measureitsgainwe operate the cavity at 77 K. The amplitudeof the signalstronglydepends on the phase The average value of the output amplitude (with respect to the input phase) and its standard deviation as functions of detuning from the resonance frequency show decaying oscillations. F. Della Valle - QFEXT 2011 - Benasque, 18-24 September 2011

  24. Parametric excitation of an external field - 4 FIRST EXPERIMENTAL RESULTS + Br ions-irradiated sample  = 7.2 ps • - stationary frequency shiftDf≈ 11 MHz • tuning the cavity, laser frepfixed G = A(lasON)/A(lasOFF) < 1---> losses df (MHz) Maximal standard deviation is observed for the same resonance frequency as the average amplitude itself F. Della Valle - QFEXT 2011 - Benasque, 18-24 September 2011

  25. Parametric excitation condition Matching the parametricresonancecondition: cavitytuning: a saffirerodchanges the cavityresonancefrequency laser tuning: active control of the M_OSC length F. Della Valle - QFEXT 2011 - Benasque, 18-24 September 2011

  26. Parametric excitation of an external field - 4 FURTHER EXPERIMENTAL RESULTS + frequency shift  28 MHz + sapphiresubstrate + mainlytuning the laser - proton-irradiated sample  = 1 ps df (MHz) df (MHz) The average value of the output amplitude and its standard deviation as functions of detuning from the resonance frequency show decaying oscillations. F. Della Valle - QFEXT 2011 - Benasque, 18-24 September 2011

  27. Parametric excitation of an external field - 5 DATA ANALYSIS AND INTERPRETATION Wefit the experimentalcurveswithrecenttheoreticalresultsobtainedbyV.V.Dodonov w is the laser frequency; w0 is the cavity frequency  phase, ||  depending on the semiconductor LOSSES Both the samples had no AR coating  more than 30% of the light is diffused in the cavity  continuous background of free carriers during the laser excitation F. Della Valle - QFEXT 2011 - Benasque, 18-24 September 2011

  28. Coming soon For a better understanding of the semiconductor Irradiation procedure–bettercontrolof the proton or ionbeam Opticalpump–terahertzprobe setup in ourlaboratory Apply the antireflectioncoatingto the “good” irradiatedsamples and repeat the gainmeasurement; Shapingof the laser pulseinsteadoftayloring the semiconductor recombinationtime F. Della Valle - QFEXT 2011 - Benasque, 18-24 September 2011

  29. Conclusions and perspectives The preliminaryresultsof the parametricamplificationof a classicalfield are coherentwiththeoreticalpredictions Once a G>1amplificationof a classicalfieldisobserved, the system is in principlereadytodetect the quantum effectvarying the cavity temperature in the range 0.8 K < T < Tc. Studyof the thermalphotonsstatistics simulation F. Della Valle - QFEXT 2011 - Benasque, 18-24 September 2011

  30. The MIR experiment: towards an in-vacuum detection of the Dynamical Casimir Effect F. Della Valle Dipartimento di Fisica, Università di Trieste, and INFN Sez. di Trieste on behalf of the MIR collaboration G. Galeazzi, G. Ruoso (LNL – PADOVA) C. Braggio, G. Carugno (PADOVA) A. Agnesi, F. Pirzio, G. Reali (PAVIA) F. Massa, D. Zanello (ROMA) F. Della Valle, G. Messineo (TRIESTE) F. Della Valle - QFEXT 2011 - Benasque, 18-24 September 2011

  31. The microwave receiver TE101 mode,101 = c/2 (b-2 + L-2) ~ 2.5 GHzEq= 10-5eV energy of a single photon RADIOMETER R H Dicke (1946) Antenna (dipole/ inductive loop) matched to the line* Thermal equilibrium Johnson noise in the resistor = blackbody rad from the walls P = 4R k f G (TR+Tn) Receiversensitivity (2  0.2) X 10-22 W/Hz F. Della Valle - QFEXT 2011 - Benasque, 18-24 September 2011

  32. Chi-squared method hp: the vacuumtermdoesnotexist “Principle of measurement” graph (fake N and fake errors!) degreesoffreeedom receiversensitivityerror thermal and vacuumphotonstatisticserror If the chi-squareis low, we can decrease the receiversensitivityerror via AVERAGING: Es: Poisson distribution; G=100  AVG  150 for each temperature If the statisticsissuper-Poissonian? F. Della Valle - QFEXT 2011 - Benasque, 18-24 September 2011

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