We show results for the expected reach of the network of experiments that is being set up globally with the aim of detecting the "invisible" axion, in light of a non-standard thermal history of the universe. Assuming that the axion is the dark matter, we discuss the reach of a successful detection by a given experimental setup in a particular axion mass window for different modifications of the cosmological background before primordial nucleosynthesis occurred. Results are presented both in the case where the present energy budget in cold axions is produced through the vacuum realignment mechanism alone, or in the case in which axionic strings also provide with additional contributions to the axion energy density. We also show that in some cosmological models, the spectrum of gravitational waves from the axionic string network would be within reach of the future network of detectors like LISA and DECIGO-BBO. We conclude that some scenarios describing the early universe can be probed jointly by the experimental efforts on axion detection and by gravity wave multi-messenger astronomy.

Holonomic quantum computation uses non-Abelian geometric phases to realize error resilient quantum gates. Nonadiabatic holonomic gates are particularly suitable to avoid unwanted decoherence effects, as they can be performed at high speed. By letting the computational system interact with a structured environment, we show that the scope of error resilience of nonadiabatic holonomic gates can be widened to include systematic parameter errors. Our scheme maintains the geometric properties of the evolution and results in an environmentassisted holonomic quantum map that can mimic the effect of a holonomic gate. We demonstrate that the sensitivity to systematic errors can be reduced in a proof-of-concept spin-bath model.Quantum holonomies are non-Abelian (non-commuting) unitary operators that only depend on paths in state space of a quantum system. The non-commuting property makes them useful for implementing quantum gates that manipulate quantum information by purely geometric means. Holonomic quantum computation (HQC) [1] is a network of holonomic gates that unifies geometric characteristics of quantum systems and information processing, as well as is conjectured to be robust to errors in experimental control parameters [2].Nonadiabatic HQC has recently been proposed [3] and experimentally implemented [4-9] as a tool to realize quantum gates based upon nonadiabatic non-Abelian geometric phases [10]. The basic setup for nonadiabatic HQC in [3] is a threelevel Λ configuration, where two simultaneous resonant laser pulses drive transitions between the qubit levels and an auxiliary state level. This scheme has been generalized to offresonant pulses [11,12]. The off-resonant setup uses two simultaneous laser pulses with the same variable detuning, which enhances the flexibility of the holonomic scheme. For experimental realization of off-resonant nonadiabatic holonomic gates, see Refs. [13][14][15][16].The nonadiabatic version of HQC avoids the drawback of the long run time associated with adiabatic holonomies [17], on which the original holonomic schemes are based [1,18]. Nonadiabatic holonomic gates are therefore particularly suitable to avoid unwanted decoherence effects [19]. The resilience to decoherence errors can be further improved by combining nonadiabatic HQC with decoherence-free subspaces [20-23] and subsystems [24], as well as dynamical decoupling [25-27]. On the other hand, it has been pointed out [28] that the original version of nonadiabatic HQC has no particular advantage compared to standard dynamical schemes in the presence of systematic errors in experimental parameters. To deal with this, we here show that the sensitivity to systematic parameter errors can be reduced by letting the system interact with a structured environment. Our approach is inspired by earlier findings [29][30][31] that transport efficiency in quantum systems can be enhanced in such environments.We modify the off-resonant non-adiabatic holonomic scheme by coupling the auxiliary state to a finite thermal bath, the latter playing t...

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We present a new probe of purely gravitationally coupled sectors with large anisotropies. These anisotropies are damped via gravitational interactions with the baryon-photon fluid, which is heated up in the process. The injected heat causes measurable distortions of the cosmic microwave background spectrum. We give analytic estimates for the size of the distortions and outline how to calculate them from first principles. These methods are applied to anisotropies in the form of a domain wall/cosmic string network or caused by a first order phase transition or scalar field dynamics. We find that this method can potentially probe large regions of previously unconstrained parameter space and is very much complementary to up-coming searches of gravitational waves caused by such dark sectors.

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