Matthew A. Hall

Fiber-based telecommunication-band source of degenerate entangled photons

We have constructed and experimentally characterized what we believe to be the first fiber-based source of degenerate polarization-entangled photon pairs in the telecommunication band. Our source design utilizes bichromatic pump pulses and an optical-fiber Sagnac loop aligned to deterministically separate degenerate photon pairs at a central wavelength. The source exhibits 0.997+/-0.006 fidelity with a maximally entangled state, measured using quantum state tomography. When reconfigured to produce identical photon pairs, the source exhibits a Hong-Ou-Mandel interference visibility of 0.97+/-0.04.

Drop-in compatible entanglement for optical-fiber networks

A growing number of quantum communication protocols require entanglement distribution among remote parties, which is best accomplished by exploiting the mature technology and extensive infrastructure of low-loss optical fiber. For this reason, a practical source of entangled photons must be drop-in compatible with optical fiber networks. Here we demonstrate such a source for the first time, in which the nonlinearity of standard single-mode fiber is utilized to yield entangled photon pairs in the 1310-nm O-band. Using an ultra-stable design, we produce polarization entanglement with 98.0% +/- 0.5% fidelity to a maximally entangled state as characterized via coincidence-basis tomography. To demonstrate the sources drop-in capability, we transmit one photon from each entangled pair through a telecommunications-grade optical amplifier set to boost classical 1550-nm (C-band) communication signals. We verify that the photon pairs experience no measurable decoherence upon passing through the active amplifier (the output states fidelity with a maximally entangled state is 98.4% +/- 1.4%).

Experimental Characterization of a Telecommunications-Band Quantum Controlled- not Gate

The quantum controlled-not gate is an example of the maximally entangling gate, which is a broad class of operations that are necessary for scalable linear optics quantum computation. Here, we characterize a telecommunications-wavelength (1550 nm) quantum controlled- not gate, and for the first time, experimentally bound its process fidelity by measuring its operation in two complementary polarization bases. The gates final process fidelity F is given by 91% ¿ F ¿ 95%.

Quantum communications: Present status and future prospects

Quantum communication entails transmission of quantum information over a classical or quantum channel, in free space or in optical fiber. This talk will focus on development of resources for efficiently implementing quantum optical communications over the standard telecom infrastructure.

Towards photonic quantum networks

We discuss O-band entangled photon pair sources and entangled photon switching technologies and their application to quantum communications and quantum information processing.

An ultra-fast optical switch for quantum networking

Quantum communications hold the promise of classically impossible communication tasks, such as the physically secure transmission of secret cryptographic keys (i.e., quantum key distribution)1 or transfer of the complete quantum state of an object to a distant location without moving the object through the intervening space (i.e., quantum teleportation)2. A key requirement for most quantum communication protocols is the successful distribution of entangled photons.3 To date, most demonstrations of quantum communications have established point-to-point links between two locations. To enable manyto-many—i.e., networked—quantum communications, a new type of switch capable of routing entangled single photons is needed. Here, we describe our progress in developing an ultrafast switch for quantum communications. Classical communications is the study of sending signals over long distances, such as electrical signals transferred over copper wires (e.g., phone lines) or optical signals transmitted through fiber-optic cables (e.g., the Internet). Although many advanced encoding and decoding techniques have been developed, at a basic level each bit of classical information is encoded as a binary choice: 0 or 1, yes or no. In contrast, a bit of quantum information can exist as a ’yes’, ’no’, or many flavors of ’maybe’. Interestingly, when quantum information is measured, the bit ceases to exist as ’maybe’ and immediately takes on a state of ’yes’ or ’no’. Entangled bits can exist in a correlated state of ’maybe’, where each will be random when measured. However, when the answers to these two measurements are compared, they will always match perfectly, i.e., both ’yes’ or both ’no’. The consequence of this behavior is that any material interacting with the photons runs the risk of destroying or degrading their fragile correlations. Since entangled correlations are exquisitely sensitive to measurement, any useful entangled photon switch must exhibit low loss and noise as well as high contrast and speed. Most importantly, it must not alter the Figure 1. Relative performance of our quantum nonlinear optical loop mirror (NOLM) switch compared to existing switching technologies in terms of noise, loss, and speed when switching polarization-entangled photons. EOM: electro-optic modulators. MEMs: microelectromechanical systems.

Two-qubit state engineering in the telecom O-band

We build and characterize a fiber-based source of 1310-nm polarization entanglement with the highest reported fidelity to a maximally entangled state, 99.6% ± 0.15% as characterized via coincidence basis tomography.

Engineering a telecom-band controlled-NOT gate

We experimentally characterize a linear optics, telecom-band quantum controlled-NOT gate using a fiber-based source of degenerate photon pairs, and bound its process fidelity to 0.907 = Fp = 0.948.

Quantum Logic Gates with Fiber-Generated Entanglement in the Telecommunications Band

Quantum states and gates in the 1.5-micron wavelength range can leverage the existing telecommunications infrastructure for communications-based quantum information processing. We present the latest results on characterization of a telecommunications-wavelength linear optics quantum controlled-NOT gate. Article not available.

Low light level V-type electromagnetically induced transparency using tapered fiber embedded in rubidium vapor

We report observation of V-type electromagntically induced transparency (EIT) at a few nW of optical power, using tapered fiber (TF) embedded in a rubidium vapor.