Probing quantum walks through coherent control of high-dimensionally entangled photons

Abstract

Control over the duration of a quantum walk is critical to unlocking its full potential for quantum search and the simulation of many-body physics. Here we report quantum walks of biphoton frequency combs where the duration of the walk, or circuit depth, is tunable over a continuous range without any change to the physical footprint of the system—a feature absent from previous photonic implementations. In our platform, entangled photon pairs hop between discrete frequency modes with the coupling between these modes mediated by electro-optic modulation of the waveguide refractive index. Through control of the phase across different modes, we demonstrate a rich variety of behavior: from walks exhibiting enhanced ballistic transport or strong energy confinement, to subspaces featuring scattering centers or local traps. We also explore the role of entanglement dimensionality in the creation of energy bound states, which illustrates the potential for these walks to quantify high-dimensional entanglement.

Nearly Perfect Transmission and Transformation of Entangled States in Topologically Protected Channels

“…The QW can be used to manipulate the quantum states. [38][39][40][41][42][43][44][45][46][47][48][49][50] The QW process is often described by introducing the evolution operator U = e −iHt , where H denotes the time-independent effective Hamiltonian over time t. Considering that the evolution operator U may be changed during the evolution, the total evolution operator U tot can be written as…”

Nonlocal subpicosecond delay metrology using spectral quantum interference

“…This scheme also offers potential for measuring relative radio frequency (RF) phase drifts in sinusoidal phase modulation applied along different fiber links. Our approach is inspired from previous studies [30][31][32][33][34] that include the characterization of spectral phase coherence in high dimensional frequency bin entangled biphotons using phase modulation and spectral filtering operations. Building on these works, here we propose and demonstrate a derived scheme, for nonlocal sensing of temporal delay and RF phase drifts without the need for low jitter SPDs.…”

Bayesian tomography of high-dimensional on-chip biphoton frequency combs with randomized measurements

“…Technologically speaking, then, our approach instead aligns more closely with recent ideas presented in EOMbased frequency-bin quantum random walks [30], where here we precede the walk with random spectral phases and consider varying circuit depths to obtain multiple pictures of the quantum state. Our experimental results show through example that such datasets are more than sufficient to converge from an initially uniform (Bures) prior to density matrices with low uncertainty and in good agreement with the expected ground truth.…”

“…1(c), with coincidences recorded over 49 signal-idler bin pairs, eight of which (bins 23-30) are selected for testing. The estimated onchip pair generation rate varies between ∼ 1.3 × 10 6 and ∼ 2.2 × 10 6 s −1 per frequency-bin pair, and the CARhere defined as the ratio of a given diagonal element to the average of all off-diagonal elements-lies in the interval [17,30] for the eight bins we test. We perform tomography for qudit dimension d ∈ {2, 3, .…”