I present results of a search for new physics performed by measuring isotope shifts (IS) in Yb+ at the Vuletić group at MIT and discuss plans to perform IS spectroscopy of Ca+ with Jonathan Home's group at ETH. Isotope shifts, when measured on at least two atomic transitions can be displayed in a King plot. The presence of nonlinearities in such a plot indicates the existence of effects beyond the expected first-order standard model (SM) contributions to the IS's. We measured IS's on three narrow transitions in five isotopes of Yb+ and observe King nonlinearity with more than 40 sigma confidence. Further, we find 4-sigma evidence that there are at least two distinct physical effects contributing to the observed nonlinearity. We identify the largest effect as originating from isotope-dependent differences in the 4th-order nuclear charge moment. We discuss possible sources of the second nonlinearity and find that it likely cannot be explained by the expected next-largest SM contribution.
Quantum phases with topological order, such as quantum spin liquids, have been the focus of explorations for several decades. Such phases feature a number of remarkable properties including long-range quantum entanglement. Moreover, they can be potentially exploited for the realization of robust quantum computation, as exemplified by the paradigmatic toric code model. While some indications that such phases may be present in frustrated condensed matter systems have been previously reported, so far quantum spin liquids have eluded direct experimental detection. In this talk, I will show how a programmable quantum simulator based on Rydberg atom arrays can be used to realize and probe quantum spin liquid states. In our approach, atoms are placed on the links of a kagome lattice and coherent evolution under Rydberg blockade enables the transition into frustrated quantum states with no local order. We detect the onset of a quantum spin liquid phase of the toric code type by measuring topological string operators in two complementary bases. The properties of this state are further revealed using a lattice with non-trivial topology, representing a step towards the realization of a topological qubit. Our observations open the door to the controlled experimental exploration of topological quantum matter, and could enable the investigation of new methods for topologically protected quantum information processing.
The Heisenberg limit of quantum measurement where the measurement precision scales as N-1 with the number of atoms N can be achieved by introducing quantum correlations between the atoms. In the present work, we show how to reach Heisenberg scaling by implementing a new Ramsey measurement scheme for cold-atom metrological devices. The proposed protocol consists of a sequence of one-axis twisting pulses and total collective spin rotations. It results in the creation of atomic Schrödinger-cat states, a superposition of two coherent spin states. Analyzing the Fisher information, we discuss the main features of the states and their interferometric precision.
State of the art atomic sensors operate near the standard quantum limit (SQL) of projection noise, and overcoming this limit by using atom-atom entanglement such as spin squeezing is a major goal in quantum metrology. By coupling an ensemble of approximately 1000 Yb-171 atoms to a high-finesse asymmetric micromirror cavity with single-atom cooperativity of 1.8., we produce a near-unitary spin squeezed state. The observed spin noise suppression and metrological gain are limited by the state readout to 9.4(4) dB and 6.5(4) dB, respectively, while the generated states offer a spin noise suppression of 15.9(6) dB and a metrological gain of 12.9(6) dB over the standard quantum limit, limited by the curvature of the Bloch sphere. When requiring the squeezing process to be within 30% of unitarity, we demonstrate an interferometer that improves the averaging time over the SQL by a factor of 3.7(2).
Although photons do no a ect each other in vacuum, interactions between individual photons could enable a wide variety of scienti c and engineering applications. Here we report on the creation of a quantum nonlinear medium with large photon-photon interactions at the single photon level. Our approach relies on Electromagnetically Induced Transparency (EIT) techniques, in which individual photons are coherently mapped onto strongly interacting Rydberg atoms. Under EIT conditions, photons traveling in the medium are best described as part-matter part-light quantum particles, called polaritons, which experience long-range interactions through the Rydberg blockade. In particular, we demonstrate coherent photon-photon interactions, akin to those associated with conventional massive particles, paving the way for novel photonics states and quantum simulation with light.
Atomic clocks have reached the Standard Quantum Limit (SQL) of precision,1 set by the projection noise
inherent in measurements on uncorrelated atoms. It is possible to overcome this limit by entangling the atoms to
generate a "squeezed state" of the atomic ensemble. We use the collective interaction of an atomic ensemble with
a far-detuned light field in an optical resonator to prepare squeezed states by two different methods: quantum
non-demolition (QND) measurement and Hamiltonian evolution. We apply both methods to an ensemble of
5 x 10487Rb atoms in a superposition of hyperfine clock states. We measure the suppression of projection
noise and compare it to the accompanying reduction in signal, thereby quantifying the net gain in spectroscopic
sensitivity.
By QND measurement, with resolution up to 9 dB below the projection noise level, we achieve 3.0(8) dB of
metrologically relevant squeezing. Whereas the measurement-based approach relies on knowledge of the (randomly
distributed) measurement outcome to produce a conditionally squeezed state, the method of Hamiltonian
evolution produces a known squeezed state independent of detector performance. We mimic the dynamics of the
one-axis twisting Hamiltonian, proposed as a generator of squeezed states by Kitagawa and Ueda,2 by using the
atom-induced frequency shift of the resonator mode and the corresponding resonator-field-induced shift of the
atomic transition frequency to introduce an effective interaction among the atoms. The resulting deterministic
squeezing is sufficient to allow a 6.0(4) dB improvement in spectroscopic sensitivity over the SQL.
Cold atoms confined inside a hollow-core photonic-crystal fiber with core diameters of a few photon wavelengths
are a promising medium for studying nonlinear optical interactions at extremely low light levels. The high electric
field intensity per photon and interaction lengths not limited by diffraction are some of the unique features of
this system. Here, we present the results of our first nonlinear optics experiments in this system including a
demonstration of an all-optical switch that is activated at energies corresponding to few hundred optical photons
per pulse.
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