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Register a new userTowards quantum entanglement of micromirrors via a two-level atom and radiation pressure
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We propose a method to entangle two distant vibrating microsize mirrors (i.e., mechanical oscillators) in a cavity optomechanical system. In this scheme, we discuss both the resonant and large-detuning conditions, and show that the entanglement of two mechanical oscillators can be achieved with the assistance of a two-level atom and cavity-radiation pressure. In the resonant case, the operation time is relatively short, which is desirable to minimize the effects of decoherence. While in the large-detuning case, the cavity is only virtually excited during the interaction. Therefore, the decay of the cavity is effectively suppressed, which makes the efficient decoherence time of the cavity to be greatly prolonged. Thus, we observe that this virtual-photon process of microscopic objects may induce the entanglement of macroscopic objects. Moreover, in both cases, the generation of entanglement is deterministic and no measurements on the atom and the cavity are required. These are experimentally important. Finally, the decoherence effect and the experimental feasibility of the proposal are briefly discussed.
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Entanglement and spontaneous emission are fundamental quantum phenomena that drive many applications of quantum physics. During the spontaneous emission of light from an excited two-level atom, the atom briefly becomes entangled with the photonic field. Here, we show that this natural process can be used to produce photon-number entangled states of light distributed in time. By exciting a quantum dot -- an artificial two-level atom -- with two sequential pi pulses, we generate a photon-number Bell state. We characterise this state using time-resolved intensity and phase correlation measurements. Furthermore, we theoretically show that applying longer sequences of pulses to a two-level atom can produce a series of multi-temporal mode entangled states with properties intrinsically related to the Fibonacci sequence. Our work demonstrates that spontaneous emission is a powerful entanglement resource and it can be further exploited to generate new states of quantum light with potential applications in quantum technologies.
Conventional information processors freely convert information between different physical carriers to process, store, or transmit information. It seems plausible that quantum information will also be held by different physical carriers in applications such as tests of fundamental physics, quantum-enhanced sensors, and quantum information processing. Quantum-controlled molecules in particular could transduce quantum information across a wide range of quantum-bit (qubit) frequencies, from a few kHz for transitions within the same rotational manifold, a few GHz for hyperfine transitions, up to a few THz for rotational transitions, to hundreds of THz for fundamental and overtone vibrational and electronic transitions, possibly all within the same molecule. Here, we report the first demonstration of entanglement between states of the rotation of a $rm^{40}CaH^+$ molecular ion and internal states of a $rm^{40}Ca^+$ atomic ion. The qubit addressed in the molecule has a frequency of either 13.4 kHz or 855 GHz, highlighting the versatility of molecular qubits. This work demonstrates how molecules can transduce quantum information between qubits with different frequencies to enable hybrid quantum systems. We anticipate that quantum control and measurement of molecules as demonstrated here will create opportunities for quantum information science, quantum sensors, fundamental and applied physics, and controlled quantum chemistry.
We prove a necessary and sufficient condition for the occurrence of entanglement in two two-level systems, simple enough to be of experimental interest. Our results are illustrated in the context of a spin star system analyzing the exact entanglement evolution of the central couple of spins.
We propose a two-qubit gate for neutral atoms in which one of the logical state components adiabatically follows a two-atom dark state formed by the laser coupling to a Rydberg state and a strong, resonant dipole-dipole exchange interaction between two Rydberg excited atoms. Our gate exhibits optimal scaling of the intrinsic error probability $E propto (Btau)^{-1}$ with the interatomic interaction strength $B$ and the Rydberg state lifetime $tau$. Moreover, the gate is resilient to variations in the interaction strength, and even for finite probability of double Rydberg excitation, the gate does not excite atomic motion and experiences no decoherence due to internal-translational entanglement.
We study quantum dissipative effects that result from the non-relativistic motion of an atom, coupled to a quantum real scalar field, in the presence of a static imperfect mirror. Our study consists of two parts: in the first, we consider accelerated motion in free space, namely, switching off the coupling to the mirror. This results in motion induced radiation, which we quantify via the vacuum persistence amplitude. In the model we use, the atom is described by a quantum harmonic oscillator (QHO). We show that its natural frequency poses a threshold which separates different regimes, involving or not the internal excitation of the oscillator, with the ulterior emission of a photon. At higher orders in the coupling to the field, pairs of photons may be created by virtue of the Dynamical Casimir Effect (DCE). In the second part, we switch on the coupling to the mirror, which we describe by localized microscopic degrees of freedom. We show that this leads to the existence of quantum contactless friction as well as to corrections to the free space emission considered in the first part. The latter are similar to the effect of a dielectric on the spontaneous emission of an excited atom. We have found that, when the atom is accelerated and close to the plate, it is crucial to take into account the losses in the dielectric in order to obtain finite results for the vacuum persistence amplitude.
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