High Efficiency in Detection of Photonic Qubits

Stefano Pirandola, Bhaskar Roy Bardhan, Tobias Gehring +2 more

Rachel Noek, Geert Vrijsen, Daniel Gaultney +4 more

Fast and efficient detection of the qubit state in trapped ion systems is critical for implementing quantum error correction and performing fundamental tests such as a loophole-free Bell test. In this work we present a simple qubit state detection protocol for a (171)Yb+ hyperfine atomic qubit trapped in a microfabricated surface trap, enabled by high collection efficiency of the scattered photons and low background photon count rate. We demonstrate average detection times of 10.5, 28.1, and 99.8 μs, corresponding to state detection fidelities of 99%, 99.856(8)%, and 99.915(7)%, respectively.

Stute, Andreas

Javid Javadzade, Majid Zahedian, Florian Kaiser +2 more

Quantum networks and distributed quantum computing rely on entanglement generation between photons and long-lived stationary qubits. For large-scale architectures, one of the most crucial parameters is the efficiency at which entanglement can be created and detected. Here, we maximize the efficiency for the detection of hybrid entanglement between a nuclear spin qubit in diamond with a photonic time-bin qubit. Our approach relies on the optimal implementation of a photonic qubit analyzer, for which we use a high-speed electro-optical deflector to direct photons deterministically along the optimal interferometer paths. This way, we eliminate all cases in which photons are randomly lost due to propagation in the wrong interferometer path. We use nitrogen-vacancy centers in diamond, for which we demonstrate nuclear spin--photon entanglement with a fidelity of 0.6 reducing the experimental acquisition time by a factor of 2. An extension to other spin--photon entanglement systems and higher-dimensional entanglement schemes is outlined.

Aaron P. VanDevender

We demonstrate the utility of frequency upconversion in a non-linear crystal for quantum information applications. By combining a bright “escort” beam with a signal photon inside of a periodically poled lithium niobate (PPLN) crystal, we are able to achieve near unit conversion efficiency. We use this conversion process to create high-efficiency infrared single-photon detectors by upconverting infrared photons to visible ones and using efficient silicon avalanche photo diodes to detect the upconverted photon. We have achieved a net system detection efficiency of 56%, far superior to previous methods for infrared photon detection. We also demonstrate the phase coherence of the upconversion process, which enables it to convert photonic qubits from one wavelength to another, potentially allowing quantum networks of disparate operating wavelengths to communicate efficiently. This quantum “transduction” feature is observed by upconverting photons passed between two unbalanced Michelson interferometers that create and measure time-bin qubits, similar to those used in many quantum cryptography systems, and verifying that the phase of the qubits is preserved. The Rabi oscillation-like behavior of upconversion is also demonstrated, allowing for the creation and manipulation of highly non-degenerate frequency qubits. These states may be used in conjunction with other degrees of freedom such as polarization, time-bin, or orbital angular momentum states to enlarge the usable single-photon Hilbert space and create a rich vocabulary for transmission of quantum information.

Peter Maunz, Steven Olmschenk, David Hayes +3 more