Polarisation entanglement storage in Diamond

Polarisation entanglement storage in Diamond

New manuscript in PRA:

Storage of polarization-entangled qubits in Diamond 

Kent Fisher, Duncan England, JP MacLean, Philip Bustard, Khabat Heshami, Kevin Resch and Ben Sussman

Bulk diamond phonons have been shown to be a versatile platform for the generation, storage, and manipulation of high-bandwidth quantum states of light. Here we demonstrate a diamond quantum memory that stores, and releases on demand, an arbitrarily polarized 250 fs duration photonic qubit. The single-mode nature of the memory is overcome by mapping the two degrees of polarization of the qubit, via Raman transitions, onto two spatially distinct optical phonon modes located in the same diamond crystal. The two modes are coherently recombined upon retrieval and quantum process tomography confirms that the memory faithfully reproduces the input state with average fidelity 0.784±0.004 with a total memory efficiency of (0.76±0.03)%. In an additional demonstration, one photon of a polarization-entangled pair is stored in the memory. We report that entanglement persists in the retrieved state for up to 1.3 ps of storage time. These results demonstrate that the diamond phonon platform can be used in concert with polarization qubits, a key requirement for polarization-encoded photonic processing.

 

 

Broadband quantum frequency conversion

Broadband quantum frequency conversion

New manuscript in PRA:

Quantum frequency conversion with ultra-broadband tuning in a Raman memory

Philip Bustard, Duncan England, Khabat Heshami, Connor Kupchak and Ben Sussman

Quantum frequency conversion is a powerful tool for the construction of hybrid quantum photonic technologies. Raman quantum memories are a promising method of conversion due to their broad bandwidths. Here we demonstrate frequency conversion of THz-bandwidth, fs-duration photons at the single-photon level using a Raman quantum memory based on the rotational levels of hydrogen molecules. We shift photons from 765 nm to wavelengths spanning from 673 to 590 nm—an absolute shift of up to 116 THz. We measure total conversion efficiencies of up to 10% and a maximum signal-to-noise ratio of 4.0(1):1, giving an expected conditional fidelity of 0.75, which exceeds the classical threshold of 2/3. Thermal noise could be eliminated by cooling with liquid nitrogen, giving noiseless conversion with wide tunability in the visible and infrared.

 

Quantum Random Number Generation

Quantum Random Number Generation

Every day we send almost 300 billion emails, and create 2.5 quintillion (2.5×1018) bytes of data. Much of this information we would readily share with others; still more is garbage, but what about the rest? Digital communications are prevalent in a many aspects of modern life where security is paramount: banking, government, commerce, national defense….

Securely sharing information is a critical challenge for modern information systems. Random numbers, random bit strings of 0’s and 1’s, are at the core of most cryptography protocols. For example, in public—private key exchange, random numbers are used to generate encryption keys. Unfortunately, random numbers are notoriously difficult to generate. In fact, most of the encryption protocols in use today rely on numbers generated using computer algorithms and are therefore pseudo-random, making them potentially vulnerable to hacking. Continue reading