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• 25 January
  [Institut Quantique] MatQ:
  25 January

  [Institut Quantique] MatQ:

  Location : Description : Meeting ID: 930 2643 2919Password: 137Thermopoweracross the phase diagram of the cuprate La1.6−xNd0.4SrxCuO4 : signatures of the pseudogap andcharge-density-wave phasesAbstract : The Seebeck coefficient(thermopower) S of the cupratesuperconductor La1.6−xNd0.4SrxCuO4 was measured across its doping phasediagram (from p= 0.12 to p=0.25), at various temperatures down to T ≈ 2K, in the normal state accessed by suppressing superconductivity with amagnetic field up to H= 37.5T. The magnitude ofS/T in the T= 0 limit is found to suddenly increase, by a factor ≈ 5,when the doping is reduced below p*= 0.23, the critical dopingfor the onset ofthe pseudogap phase. This confirms that the pseudogap phase causes a largereduction of the carrierdensity n, consistent with a dropfrom n= 1 +p above p* ton=p below p*, as previously inferred from measurements of the Hallcoefficient, resistivity and thermal conductivity. When the doping is reduced below p= 0.19,a qualitative change is observed wherebyS/T decreases as T→0,eventuallyto reach negative values at T=0. In prior work on other cuprates, negative values of S/T atT→0 were shown to result froma reconstruction of the Fermi surface caused by charge-density-wave (CDW) order. We thereforeidentify pCDW ≈ 0.19as the critical doping beyond whichthere is no CDW-induced Fermi surface reconstruction. The fact that pCDW is well separated from p* revealsthat there is a doping range below p* where the transport signatures of thepseudogap phase are unaffectedby CDW correlations, as previously found in YBa2Cu3Oy and La2−xSrxCuO4. 

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• 25 January
  [Institut Quantique] Séminaire de l’IQ : Honghao Fu
  25 January

  [Institut Quantique] Séminaire de l’IQ : Honghao Fu

  Location : Description : Rejoindre la réunion Microsoft Teams / Join the Microsoft Teams meetingHonghao FuTitre : Quantum correlations: applications and characterization.Résumé :The study of quantum correlations goes back to the 1960s, when John Bell first observed that local measurements on an entangled system can give rise to a nonlocal correlation (J. Bell Physics, 1964). Studies of quantum correlations have led to exciting demonstrations of the quantum advantage. My research focuses on the applications of quantum correlations in device-independent cryptography, and the characterization of quantum correlations. I will first introduce device-independent randomness generation and randomness expansion protocols, which have been realized in experiments. Then, I will discuss how quantum correlations allow us to test an unknown quantum device with pure classical interactions. Lastly, the conceptual question about quantum correlations is whether we can get a finite-length description of the set of quantum correlations of the same size. I will try to answer it from the computational complexity perspective.

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• 27 January
  [Institut Quantique] Séminaire de l’IQ : Philippe Lewalle
  27 January

  [Institut Quantique] Séminaire de l’IQ : Philippe Lewalle

  Location : Description : Rejoindre la réunion Microsoft Teams / Join the Microsoft Teams meetingPhilippe LewalleUniversity of RochesterInvité d'Alexandre BlaisTitre/TitleRésumé/Abstract  

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