Entanglement of distinguishable quantum memories

Abstract

Time-resolved photon detection can be used to generate entanglement between distinguishable photons. This technique can be extended to entangle quantum memories that emit photons with different frequencies and identical temporal profiles without the loss of entanglement rate or fidelity. We experimentally realize this process using remotely trapped 171 Yb + ions where heralded entanglement is generated by interfering distinguishable photons. This technique may be necessary for future modular quantum systems and networks that are composed of heterogeneous qubits.PACS numbers: 03.67.Bg, 37.10.TyThe entanglement of remote quantum memories via photons is an enabling technology for modular quantum computing, transmission of quantum information, and networked quantum timekeeping [1][2][3][4][5]. All of these applications rely on the excellent control and long-lived coherence properties of quantum memories and the ease with which photons can be used to distribute both entanglement and quantum information.Currently, photon-mediated entanglement of remote quantum memories has only been achieved using heralded schemes; atomic ensembles [6], trapped ions [7], single neutral atoms in optical cavities [8], and nitrogen vacancy centers in diamond [9] have all been entangled in this manner. However, heralded entanglement is possible in these systems because the memories inherently emit indistinguishable photons or can be manipulated to do so. This requirement of photon indistinguishability is a major impediment to the construction of heterogeneous quantum networks and also hinders the entanglement of similar memories whose emission frequencies differ due to variations in local environment or fabrication. Recently, photons with frequencies that differ by many linewidths have been entangled using time-resolved detection and active feedforward [10]. Here, we extend this technique to entangle distinguishable remote quantum memories by interference of distinguishable photons.In order to generate heralded entanglement of remote quantum memories, photons emitted from each memory enter a partial Bell state analyzer where they interfere on a beamsplitter and are subsequently detected, projecting the memories into a corresponding entangled state. If the photons are identical, the memories will be projected into a known Bell state [11]. However, if the photons are distinguishable, the resulting entangled memory state will have some additional phase factor or unequal probability amplitudes. Here we assume that quantum memories labeled A and B emit photons with identical temporal profiles but frequencies that differ by ∆ω for a given polarization [12]. These two photons are detected within the Bell state analyzer a time ∆t apart, projecting the memories into a Bell state with a time-dependent phase, e.g.,), where {|0 ,|1 } are the computational basis states of each memory. The temporal resolution t r of the photon detection circuit determines how precisely the phase ∆ω∆t is known since the phase is probabilistically distributed over an in...

Microwave-activated controlled- Z gate for fixed-frequency fluxonium qubits

“…Such a separation of states for information storage and processing allows one to perform many high-fidelity gates before the qubit state is spoiled by decoherence. This was realized in architectures based on nitrogen-vacancy centers [15], trapped ions [16], and Rydberg atoms [17]. In superconducting systems, a similar idea was implemented in experiments where the qubit quantum state is stored in a high-quality microwave resonator [18,19], while the physical superconducting qubits are used only for short times during gate realizations.…”

Polarisation-preserving photon frequency conversion from a trapped-ion-compatible wavelength to the telecom C-band

“…Another challenge is that ionic transitions are fixed and narrowband, such that, except in rare cases [8], they cannot be interfaced with other examples of quantum matter to enable new ion-hybrid quantum systems [9]. Note that frequency-distinguishable quantum systems can be linked via their photons, though at the cost of reducing the efficiency of making that link [10].…”

“…Another challenge is that ionic transitions are fixed and narrowband, such that, except in rare cases [8], they cannot be interfaced with other examples of quantum matter to enable new ion-hybrid quantum systems [9]. Note that frequency-distinguishable quantum systems can be linked via their photons, though at the cost of reducing the efficiency of making that link [10].The aforementioned challenges could be overcome using quantum frequency conversion (QFC) [11,12]; a nonlinear optical process in which a photon of one frequency is converted to another, whilst preserving all the quantum and classical photon properties. QFC of single photons has recently been studied in a variety of contexts [13][14][15][16][17][18] and is typically achieved using three-wave mixing in a secondorder non-linear ( 2 ) crystal.…”

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