54 research outputs found
Observation of Bulk Fermi Arc and Polarization Half Charge from Paired Exceptional Points
The ideas of topology have found tremendous success in Hermitian physical
systems, but even richer properties exist in the more general non-Hermitian
framework. Here, we theoretically propose and experimentally demonstrate a new
topologically-protected bulk Fermi arc which---unlike the well-known surface
Fermi arcs arising from Weyl points in Hermitian systems---develops from
non-Hermitian radiative losses in photonic crystal slabs. Moreover, we discover
half-integer topological charges in the polarization of far-field radiation
around the Fermi arc. We show that both phenomena are direct consequences of
the non-Hermitian topological properties of exceptional points, where
resonances coincide in their frequencies and linewidths. Our work connects the
fields of topological photonics, non-Hermitian physics and singular optics, and
paves the way for future exploration of non-Hermitian topological systems.Comment: 7 pages, 4 figure
Nano-acoustic resonator with ultralong phonon lifetime
The energy damping time in a mechanical resonator is critical to many precision metrology applications, such as timekeeping and force measurements. We present measurements of the phonon lifetime of a microwave-frequency, nanoscale silicon acoustic cavity incorporating a phononic bandgap acoustic shield. Using pulsed laser light to excite a colocalized optical mode of the cavity, we measured the internal acoustic modes with single-phonon sensitivity down to millikelvin temperatures, yielding a phonon lifetime of up to τ_(ph,0) ≈ 1.5 seconds (quality factor Q = 5 × 10¹⁰) and a coherence time of τ_(coh,0) ≈ 130 microseconds for bandgap-shielded cavities. These acoustically engineered nanoscale structures provide a window into the material origins of quantum noise and have potential applications ranging from tests of various collapse models of quantum mechanics to miniature quantum memory elements in hybrid superconducting quantum circuits
Nano-acoustic resonator with ultralong phonon lifetime
The energy damping time in a mechanical resonator is critical to many precision metrology applications, such as timekeeping and force measurements. We present measurements of the phonon lifetime of a microwave-frequency, nanoscale silicon acoustic cavity incorporating a phononic bandgap acoustic shield. Using pulsed laser light to excite a colocalized optical mode of the cavity, we measured the internal acoustic modes with single-phonon sensitivity down to millikelvin temperatures, yielding a phonon lifetime of up to τ_(ph,0) ≈ 1.5 seconds (quality factor Q = 5 × 10¹⁰) and a coherence time of τ_(coh,0) ≈ 130 microseconds for bandgap-shielded cavities. These acoustically engineered nanoscale structures provide a window into the material origins of quantum noise and have potential applications ranging from tests of various collapse models of quantum mechanics to miniature quantum memory elements in hybrid superconducting quantum circuits
Perfect single-sided radiation and absorption without mirrors
Highly directional radiation from photonic structures is important for many applications, including high-power photonic crystal surface-emitting lasers, grating couplers, and light detection and ranging devices. However, previous dielectric, few-layer designs only achieved moderate asymmetry ratios, and a fundamental understanding of bounds on asymmetric radiation from arbitrary structures is still lacking. Here, we show that breaking the 180° rotational symmetry of the structure is crucial for achieving highly asymmetric radiation. We develop a general temporal coupled-mode theory formalism to derive bounds on the asymmetric decay rates to the top and bottom of a photonic crystal slab for a resonance with arbitrary in-plane wavevector. Guided by this formalism, we show that infinite asymmetry is still achievable even without the need for back-reflection mirrors, and we provide numerical examples of designs that achieve asymmetry ratios exceeding 10[superscript 4]. The emission direction can also be rapidly switched from top to bottom by tuning the wavevector or frequency. Furthermore, we show that with the addition of weak material absorption loss, such structures can be used to achieve perfect absorption with single-sided illumination, even for single-pass material absorption rates less than 0.5% and without back-reflection mirrors. Our work provides new design principles for achieving highly directional radiation and perfect absorption in photonics.United States. Army Research Office. Institute for Soldier Nanotechnologies (Grant W911NF-13- D0001)Solid-State Solar-Thermal Energy Conversion Center (Grant DESC0001299)United States-Israel Binational Science Foundation (Grant 2013508)National Science Foundation (U.S.) (Grant DMR-1307632
Constant-Overhead Fault-Tolerant Quantum Computation with Reconfigurable Atom Arrays
Quantum low-density parity-check (qLDPC) codes can achieve high encoding
rates and good code distance scaling, providing a promising route to
low-overhead fault-tolerant quantum computing. However, the long-range
connectivity required to implement such codes makes their physical realization
challenging. Here, we propose a hardware-efficient scheme to perform
fault-tolerant quantum computation with high-rate qLDPC codes on reconfigurable
atom arrays, directly compatible with recently demonstrated experimental
capabilities. Our approach utilizes the product structure inherent in many
qLDPC codes to implement the non-local syndrome extraction circuit via atom
rearrangement, resulting in effectively constant overhead in practically
relevant regimes. We prove the fault tolerance of these protocols, perform
circuit-level simulations of memory and logical operations with these codes,
and find that our qLDPC-based architecture starts to outperform the surface
code with as few as several hundred physical qubits at a realistic physical
error rate of . We further find that less than 3000 physical qubits
are sufficient to obtain over an order of magnitude qubit savings compared to
the surface code, and quantum algorithms involving thousands of logical qubits
can be performed using less than physical qubits. Our work paves the way
for explorations of low-overhead quantum computing with qLDPC codes at a
practical scale, based on current experimental technologies
Controlling local thermalization dynamics in a Floquet-engineered dipolar ensemble
Understanding the microscopic mechanisms of thermalization in closed quantum
systems is among the key challenges in modern quantum many-body physics. We
demonstrate a method to probe local thermalization in a large-scale many-body
system by exploiting its inherent disorder, and use this to uncover the
thermalization mechanisms in a three-dimensional, dipolar-interacting spin
system with tunable interactions. Utilizing advanced Hamiltonian engineering
techniques to explore a range of spin Hamiltonians, we observe a striking
change in the characteristic shape and timescale of local correlation decay as
we vary the engineered exchange anisotropy. We show that these observations
originate from the system's intrinsic many-body dynamics and reveal the
signatures of conservation laws within localized clusters of spins, which do
not readily manifest using global probes. Our method provides an exquisite lens
into the tunable nature of local thermalization dynamics, and enables detailed
studies of scrambling, thermalization and hydrodynamics in strongly-interacting
quantum systems.Comment: 6 pages, 4 figures main tex
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