The efficient conversion of thermal energy to mechanical work by a heat engine is an ongoing technological challenge. Since the pioneering work of Carnot, it is known that the efficiency of heat engines is bounded by a fundamental upper limit -the Carnot limit. Theoretical studies suggest that heat engines may be operated beyond the Carnot limit by exploiting stationary, nonequilibrium reservoirs that are characterized by a temperature as well as further parameters. In a proof-of-principle experiment, we demonstrate that the efficiency of a nano-beam heat engine coupled to squeezed thermal noise is not bounded by the standard Carnot limit. Remarkably, we also show that it is possible to design a cyclic process that allows for extraction of mechanical work from a single squeezed thermal reservoir. Our results demonstrate a qualitatively new regime of non-equilibrium thermodynamics at small scales and provide a new perspective on the design of efficient, highly miniaturized engines.

Quantum entanglement emerges naturally in interacting quantum systems and plays a central role in quantum information processing [1][2][3][4] . But the generation of entanglement does not require direct interactions: single-photon detection in spin-flip Raman scattering projects two distant spins onto a maximally entangled state, provided that it is impossible to determine the source of the detected photon 5 . Here, we demonstrate such heralded quantum entanglement [6][7][8][9] of two quantum-dot hole spins separated by 5 m using single-photon interference. Thanks to fast spin initialization in 10 ns, hole-spin coherence lasting ∼40 ns and e cient photon extraction from dots [10][11][12] embedded in leaky microcavity structures, we generate 2,300 entangled spin pairs per second, which represents a 1,000-fold improvement as compared to previous experiments 13. The delayed two-photon interference scheme we developed allows the e cient verification of quantum correlations. Combined with schemes for transferring quantum information to a long-lived memory qubit 14 , fast entanglement generation could impact quantum repeater architectures.In contrast to previous experiments demonstrating electron spin photon entanglement [10][11][12] , our experiments are based on heavyhole pseudo-spins in self-assembled quantum dots (QD) that have been shown to exhibit long coherence times [15][16][17][18] . Figure 1a depicts our experimental set-up, incorporating two QDs separated by 5 m that are resonantly driven by weak 3.2 ns-long pulses from a Ti:Sapphire laser, termed the entanglement laser. Additional diode laser pulses ensure that each QD is optically charged with a single excess heavy hole and that the hole pseudo-spin is prepared in the requisite state. The QDs are embedded in distributed Bragg reflector (DBR) structures 19 which, together with a ZnO solid immersion lens, allow efficient (∼20%) collection of the generated resonance fluorescence. Figure 1b shows the relevant energy-level diagram as well as the allowed optical transitions for single-hole charged QDs when an external magnetic field (B x ) is applied perpendicular to the growth direction (Voigt geometry; refs 20,21). The initial states of the optical transitions in the single-hole charged regime are metastable states identified by the orientation of the heavy-hole pseudo-spin, with |⇑ (|⇓ ) denoting +3/2 (−3/2) hole angular momentum projection. The presence of B x = 0 yields a finite splitting of the pseudo-spin states due to heavy-light hole mixing 22 . Spontaneous emission of a V (H) polarized photon at frequency ω blue (ω diag1 ) from the trion state |T b at rate Γ /2 brings the QD back into the |⇓ (|⇑ ) state. Owing to these selection rules, addressing any of the four allowed transitions with a single laser will efficiently transfer the spin population into the opposite ground state within 10 ns (see Supplementary information). As the intensity of the entanglement laser is chosen to be well below saturation, the ensuing optical transitions lead to either V-...

The interaction between a single confined spin Even though recent experiments have established this system as a new paradigm for solid-state quantum optics, all of the striking experimental observations to date could be understood within the framework of single-or few-particle physics enriched by perturbative coupling to reservoirs involving either phonons, a degenerate electron gas [7,8], or nuclear spins [9,10]).We present differential transmission (DT)

Light-matter interaction has played a central role in understanding as well as engineering new states of matter. Reversible coupling of excitons and photons enabled groundbreaking results in condensation and superfluidity of nonequilibrium quasiparticles with a photonic component. We investigated such cavity-polaritons in the presence of a high-mobility two-dimensional electron gas, exhibiting strongly correlated phases. When the cavity was on resonance with the Fermi level, we observed previously unknown many-body physics associated with a dynamical hole-scattering potential. In finite magnetic fields, polaritons show distinct signatures of integer and fractional quantum Hall ground states. Our results lay the groundwork for probing nonequilibrium dynamics of quantum Hall states and exploiting the electron density dependence of polariton splitting so as to obtain ultrastrong optical nonlinearities.

Nonperturbative coupling between cavity photons and excitons leads to formation of hybrid light-matter excitations termed polaritons. In structures where photon absorption leads to creation of excitons with aligned permanent dipoles [1-3], the elementary excitations, termed dipolar polaritons, are expected to exhibit enhanced interactions [4, 5]. Here, we report a substantial increase in interaction strength between dipolar polaritons as the size of the dipole is increased by tuning the applied gate voltage. To this end, we use coupled quantum well structures embedded inside a microcavity where coherent electron tunneling between the wells controls the size of the excitonic dipole. Modifications of the interaction strength are characterized by measuring the changes in the reflected intensity of light when polaritons are driven with a resonant laser. Factor of 6.5 increase in the interaction strength to linewidth ratio that we obtain indicates that dipolar polaritons could be used to demonstrate a polariton blockade effect [6] and thereby form the building blocks of many-body states of light [7].