Giant atom enables valley-polarized photon emission

This approach results in photons acquiring a defined valley character and chiral emission along domain walls created within the lattice. This provides a promising route toward implementation of single-photon disorder-robust chiral emission without breaking time-reversal symmetry of the electromagnetic medium in platforms such as circuit QED.

Giant Atoms Enable Selective Valley Coupling in Honeycomb Lattices Engineered coupling points dictate which photonic valley receives emitted light, allowing for precise control over the quantum state of individual photons. This selectivity stems from the creation of what researchers term a “giant atom,” a qubit intricately linked to a honeycomb lattice of resonators. Recent experimental work has demonstrated complex, phase-tunable coupling between the qubit and multiple resonators. The ability to selectively couple to a single valley is a key property of these giant atoms, differing significantly from conventional light-matter interactions. In a standard setup, a qubit might couple equally to all photonic modes; however, this engineered system enables suppression of coupling to specific valleys while preserving it for others. This is achieved by inverting equations to express the interaction Hamiltonian in terms of normal modes, allowing researchers to tailor the coupling to specific photonic characteristics. Spontaneous emission from this giant atom exhibits a distinct polarization dependent on the coupling geometry, confirming the effectiveness of the selective coupling mechanism. Analysis of the emitted field reveals that a contour vanishes around a specific point in the lattice when the emission phase is set to π/3, effectively directing photons into a single valley. Conversely, setting the phase to -π/3 suppresses the contour around a different point, demonstrating the ability to switch between valley preferences.

The team further demonstrated chiral emission, where photons travel in a single direction, by strategically positioning the qubit near a domain wall within the honeycomb lattice. This domain wall exists between regions with opposite sublattice detuning, supporting valley-polarized edge modes. When the giant atom decouples from a specific valley, it cannot emit into the corresponding edge-mode band, resulting in unidirectional photon emission along the domain wall. For coupling points with specific strengths and a phase difference, the decay rate of the emitted photons matches theoretical predictions. “By exploiting the non-local character of the emitter–bath coupling, interference among different coupling points can be engineered so as to suppress the coupling to one valley while preserving it to the other,” the researchers state in their published work, highlighting the fundamental advantage of this approach. This ability to manipulate valley-selective light-matter interactions in synthetic photonic lattices offers a new avenue for quantum optics, potentially enabling robust, disorder-resistant single-photon emission without disrupting the electromagnetic medium’s time-reversal symmetry. The work establishes giant atoms as a powerful tool for controlling light at the quantum level, opening possibilities for advanced photonic devices and quantum information processing. Valleytronics and Valley Photonics: Encoding Information with Photonic Valleys By precisely tailoring the geometry of how the emitter connects to the lattice, researchers achieved selective emission into a single valley, a key step toward manipulating information encoded in the valley degree of freedom. This selective emission is distinct from simply polarizing valley characteristics, representing control over which valley the light enters. The engineered system uses the principle that inequivalent extrema in materials like graphene define a valley degree of freedom, and that breaking inversion symmetry imparts opposite Berry curvature and orbital magnetic moment to these valleys. This phenomenon, analogous to the valley Hall effect observed in both materials and photonics, underpins the ability to create valley-polarized edge modes, channels localized at interfaces between regions of opposite valley topology.

The team demonstrated that by positioning the giant atom near a domain wall supporting these modes, emitted photons exhibited chiral behavior, traveling in a single direction along the wall. This chirality arises not from breaking time-reversal symmetry within the photonic environment, but from the phase-patterned coupling between the giant atom and the field. A critical condition for decoupling the giant atom from a specific valley was identified, ensuring that emission is restricted to the desired valley. This decoupling is fundamental to achieving the observed valley selectivity, allowing the giant atom to function as a source of valley-polarized photons, unlike a standard atom which would populate both valleys equally. “In contrast, a normal atom, which couples equally to both valleys, emits the photon along the domain wall, with equal probability in the two opposite directions,” the researchers write. The implications of this work extend beyond fundamental quantum optics, potentially enabling new approaches to quantum-optical applications and phenomena based on the valley degree of freedom of photons. Nonlocal Coupling: Engineering Giant Atom Emission Characteristics The ability to control which photonic valley a photon occupies relies on precise manipulation of light-matter interactions, and recent work demonstrates a pathway to achieve this through engineered coupling points within a honeycomb lattice. For two coupling points, this decoupling hinges on a relative phase difference of either π/3 or -π/3, conditions that are achievable with a giant atom. Numerical simulations corroborate these analytical predictions, demonstrating strongly valley-polarized radiation in momentum space when these conditions are met.

The team’s work shows that for a specific phase, the contour around one valley vanishes for the emitted field, confirming the validity of the selective coupling condition. The researchers further investigated spontaneous emission in a homogeneous honeycomb lattice, observing that the emitted radiation becomes strongly valley-polarized in momentum space. This polarization is achieved through selective coupling to either the K or K’ valley, a result directly linked to the decoupling condition established earlier. Valley-Polarized Emission in Bulk Photonic Structures The ability to maintain time-reversal symmetry while achieving chiral photon emission represents a departure from conventional approaches requiring symmetry breaking throughout the entire photonic lattice. Unlike previous designs, the work detailed demonstrates this emission is possible by confining symmetry breaking to the light-matter coupling itself, and requires only two coupling points, one with a complex coupling amplitude. This simplification offers a pathway toward scalable quantum photonic devices. This selectivity stems from the specific geometry of the coupling points, and is governed by a decoupling condition where emission into a specific valley is suppressed when the giant atom is decoupled from it. The researchers further explored the behavior of both normal atoms and giant atoms within a homogeneous honeycomb lattice. They found that for large decays, the rate asymptotically approaches a value dependent on the coupling strength. This finding is significant because it establishes a clear relationship between the engineered coupling and the efficiency of valley-polarized emission. By combining this valley-polarized photonic environment with the selective valley coupling enabled by the giant atom, the team demonstrated chiral spontaneous emission. Depending on the engineered relative phases between the coupling-point strengths, the photon is emitted preferentially into one propagation direction along the domain wall. For example, with coupling strengths of g1 = g/ 2 and g2 = g1eiφ, the decay rate can be precisely tuned. The system could facilitate effective interactions mediated by valley-polarized edge channels, opening possibilities for novel quantum information processing architectures. Chiral Single-Photon Emission at Topological Domain Walls The ability to control the direction of single photons emitted from a quantum system relies on carefully engineered material properties, as demonstrated by a recent exploration of honeycomb photonic lattices. This directional emission stems from the interplay between the qubit’s coupling to the lattice and the presence of valley-polarized edge modes at the domain wall interface. A key element enabling this control is the creation of a “giant atom” by coupling a qubit to the honeycomb lattice in a non-local manner. This giant atom isn’t a physically larger atom, but rather an effective emitter with enhanced interaction with the surrounding photonic environment. By tailoring the geometry of these coupling points, the giant atom can be made to selectively interact with only one of two valleys within the lattice’s energy structure, imprinting the associated Berry curvature onto the emitted photon. This selective coupling is essential for achieving the desired valley polarization and ultimately, chiral emission. However, the engineered giant atom circumvents this limitation. This precise control over the emission process opens possibilities for advanced quantum technologies. “In summary, we have shown that a giant atom coupled to a photonic graphene lattice can be used to engineer selective coupling to a single valley and, in the presence of valley-polarized edge modes, to realize chiral single-photon emission without requiring time-reversal-symmetry breaking in the bath,” the researchers state. The ability to achieve chiral emission without breaking time-reversal symmetry is particularly significant, as it avoids the need for external magnetic fields or other symmetry-breaking elements that can introduce unwanted noise and decoherence. Source: https://iopscience.iop.org/article/10.1088/2058-9565/aebe5c More like thisQuantum PhysicsQuantum operations guide shows how physics limits information processingQuantum PhysicsAnderson orthogonality catastrophe is seen in quantum dot experimentsQuantum Research NewsPhysicists demonstrate a spin-state memory for quantum informationPhysicsResidual coherence dominates entanglement in neutrino oscillation, study findsStay currentSee today’s quantum computing news on Quantum Zeitgeist for the latest breakthroughs in qubits, hardware, algorithms, and industry deals. Tags: