Quantum Memory

A quantum memory is a stationary system or device, which can maintain a quantum state for a desired amount of time after which the state must be able to be read out either in the form or a non-stationary quantum system or via a classical projection measurement. In that sense, quantum memory is relevant for networks if the quantum state can be mapped either from or to (ideally both) a non-stationary system carrying the quantum state, which in essence means an optical photon. When gauging the quality of quantum memory, according to e.g. its storage efficiency, time, fidelity, bandwidth and multimode capacity, it is important to optimize according to the properties that matter for the particular application. As an example, for quantum memory used to buffer qubits in an optical quantum processor the storage time may be less of a concern than the bandwidth. The research in the QCloudLab focuses on developing efficient quantum memory for quantum repeaters.

Optical quantum memory has been implemented in diverse physical systems such as warm-gasses [BJ04], single-trapped atoms [HPS11], diamond colour centres [AR16], and rare-earth ion (REI) doped materials [JJL05, BK06, MA09], to name a few. REI materials have many desirable properties for quantum memory. They can feature very long coherence times – up to several ms on optical transitions and several hours on spin transitions – which allows optical storage that may be transferred to spin transitions. The collective enhancement leads to large photon absorption probabilities, which yield fast optical interaction. The inhomogeneous broadening translates into large memory bandwidths and multimode storage capacity. The existence of long-lived shelving levels allows for spectral tailoring as is needed in many photon-echo type quantum memories.

In the QCloudLab we focus on the Atomic Frequency Comb protocol [MA09] due to its important and unique multi-mode storage capacity and large bandwidth. Past work at the UofC resulted in the first demonstration of entangled photon-storage in a solid-state material using a waveguide defined in a thulium doped lithium-niobate (Tm:LiNbO3) crystal. This was followed by a demonstration of storage of entangled telecom-wavelength photons in a erbium doped silica fibre (Er:SiO2) and finally simultaneous storage of both entangled photons of a pair – one in Tm:LiNbO3 and one in Er:SiO2. Other experiments have shown preservation of indistinguishability of stored photons, storage of polarization qubits encoded in heralded single photons at telecom wavelength, storage of telecom wavelength photons in erbium doped lithium niobite waveguides using super-hyperfine levels, and spectrally multimode storage in Tm:LiNbO3. These demonstrations of quantum memory are based on detailed spectroscopic studies of the materials, which is an ongoing research direction in the QCloudLab.

Current projects:

 

References – Quantum Memory

[AR16]         A Reiserer, N Kalb, MS Blok, et al., Phys. Rev. X 6, 021040 (2016)

[BJ04]          B Julsgaard, J Sherson, JI Cirac, et al., Nature 432, 482 (2004)

[BK06]         B. Kraus, W. Tittel, N. Gisin, et al., Phys. Rev. A 73, 020302(R) (2006)

[CWT14a]    C W Thiel, N Sinclair, W Tittel, and R L Cone, Phys. Rev. Lett. 113, 160501 (2014)

[CWT14b]    C W Thiel, N Sinclair, W Tittel, and R L Cone, Phys. Rev. B 90, 214301 (2014)

[HPS11]       H P Specht, C Nölleke, A Reiserer, et al., Nature 473, 190 (2011)

[JJL05]         J J Longdell, E Fraval, M J Sellars, NB Manson, Phys. Rev. Lett. 95 (6), 063601

[MA09]        M Afzelius, C Simon, H De Riedmatten, N Gisin, Phys. Rev. A 79, 052329 (2009)

[MA10]        M Afzelius, C Simon, Phys. Rev. A 82, 022310 (2010)

[MS13]        M.  Sabooni, Q. Li, S. Kroll, L. Rippe, Phys. Rev. Lett., 110, 133604 (2013)

[NS18]         N Sinclair, D Oblak, et al., Unpublished

[PJ14]          P.  Jobez, et al., New J. Phys. 16, 083005 (2014)