Interfacing photonic and solid-state qubits within a hybrid quantum architecture offers a promising route towards large scale distributed quantum computing. Ideal candidates for coherent qubit interconversion are optically active spins, magnetically coupled to a superconducting resonator. We report on an on-chip cavity QED experiment with magnetically anisotropic Er(3+)∶Y2SiO5 crystals and demonstrate collective strong coupling of rare-earth spins to a lumped element resonator. Moreover, the electron spin resonance and relaxation dynamics of the erbium spins are detected via direct microwave absorption, without the aid of a cavity.

An important desired ingredient of superconducting quantum circuits is a readout scheme whose complexity does not increase with the number of qubits involved in the measurement. Here, we present a readout scheme employing a single microwave line, which enables simultaneous readout of multiple qubits. Consequently, scaling up superconducting qubit circuits is no longer limited by the readout apparatus. Parallel readout of 6 flux qubits using a frequency division multiplexing technique is demonstrated, as well as simultaneous manipulation and time resolved measurement of 3 qubits. We discuss how this technique can be scaled up to read out hundreds of qubits on a chip.

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Random numbers are required for a variety of applications from secure communications to MonteCarlo simulation. Yet randomness is an asymptotic property and no output string generated by a physical device can be strictly proven to be random. We report an experimental realization of a quantum random number generator (QRNG) with randomness certified by quantum contextuality and the Kochen-Specker theorem. The certification is not performed in a device-independent way but through a rigorous theoretical proof of each outcome being value-indefinite even in the presence of experimental imperfections. The analysis of the generated data confirms the incomputable nature of our QRNG.While we can consider a mathematical abstraction of a true random number generator and examine its properties, in the physical world we are confined to performing finite statistical tests on the output strings. By applying sets of such tests (like NIST [1] or diehard [2]) we can verify with arbitrarily high probability that the generator is NOT random (if it has failed at least one test), but cannot prove its randomness in the opposite case. As an example, one may construct a pseudo-random number generator which passes all above-mentioned tests while the produced sequence is deterministic and even computable [3]. The impossibility of a rigorous proof of randomness for a finite string generated by a physical device motivates the consideration of more fundamental arguments to support a RNG's randomness. From this point of view, no classical RNG may be truly random as it is deterministic by the laws of classical mechanics, and may in principle be predicted. A natural foundation to build a RNG would be quantum theory, as it is intrinsically random.However, although quantum mechanics obeys probabilistic rules, the possibility of separating intrinsic randomness from apparent randomness arising from a lack of control or from experimental noise is still under debate [4]. Moreover, while quantum mechanics for a two-level system is described by the same intrinsically-probabilistic measurement rules, one may not strictly prove valueindefiniteness, and hence indeterminism, of its results [5].These considerations led to the next advance in quantum number generation: the protocols certified by violation of certain Bell-type inequalities [6][7][8]. More specifically, through violation of the CHSH inequality one may certify that the observed outputs are not entirely predetermined and write a lower bound on the generating process entropy. Unfortunately, this approach does not allow one to close the gap between this lower bound and true randomness. In addition, the Bell-type certification schemes can be regarded as random expanders rather than generators due to the requirement of "a small private random seed" to operate [6,9,10]. Finally, the random number generators certified by Bell inequalities utilize no-signaling assumption and is, therefore, inherently a non-local device which is challenging to use for practical applications.To address this problem, a diff...