Space QUEST mission proposal: experimentally testing decoherence due to gravity

Abstract

Models of quantum systems on curved space-times lack sufficient experimental verification. Some speculative theories suggest that quantum correlations, such as entanglement, may exhibit different behavior to purely classical correlations in curved space. By measuring this effect or lack thereof, we can test the hypotheses behind several such models. For instance, as predicted by Ralph et al [5] and Ralph and Pienaar [1], a bipartite entangled system could decohere if each particle traversed through a different gravitational field gradient. We propose to study this effect in a ground to space uplink scenario. We extend the above theoretical predictions of Ralph and coworkers and discuss the scientific consequences of detecting/failing to detect the predicted gravitational decoherence. We present a detailed mission design of the European Space Agency's Space QUEST (Space-Quantum Entanglement Space Test) mission, and study the feasibility of the mission scheme.

Spaceborne, low-noise, single-photon detection for satellite-based quantum communications

“…For an operating temperature of -12°C and for an excess voltage of 17 V, the DCR sensitivity is 42 1.00 10 cps cm / proton   (50 MeV). Combined with the estimated in-orbit radiation dose, the DCR increase is ~219 cps/day, which is too high for several space applications, including quantum communications [9][10][11][12][13][14][15][16]. In addition to DCRs, we also measured the APD breakdown voltage, responsivity, and dark current.…”

“…Single-photon detectors (SPDs) have been extensively used as one of the key components in extremely weak light detectionn applications over the past two decades. These include light detection and ranging [1][2][3], laser time transfer [4,5], scintillation detection of elementary particles [6], deep-space optical communications [7,8], and quantum communications [9][10][11][12][13][14][15][16]. Among these applications, quantum communications constitute the most rigorous application that demands increased SPD detection efficiency (DE) and low-dark count rate (DCR), given that the optical signal cannot be amplified like classical light signals according to the quantum noncloning principle [17] to guarantee the high fidelity of the single photon during its transmission.…”

Nanobob: a cubesat mission concept for quantum communication experiments in an uplink configuration

“…SPDC is not very efficient. The Vienna source can generate up to about 8·10 6 pairs per second per mW of pump power, for a maximum pair generation rate of 3·10 8 s -1 [4]. Improving the brightness of the source would enable increasing the key rate of the QKD protocol (see section 1.7).…”

“…The Fried parameter r0 corresponds to the diameter of the diffraction limited telescope in the absence of atmospheric turbulence that would yield the same resolution as a telescope with a diameter much larger than r0 but in the presence of the turbulent atmosphere [62]. It may be written as [63]: (4) where is the (temperature-dependent) atmospheric turbulence strength at the position z along the light path. When the path is a straight line along a zenith angle ζ, the path is longer by a factor approximately equal to 1/cos(ζ), leading to a smaller Fried parameter:…”

“…This in turn may require that the photon flux arriving at Alice be distributed over a large number of individual detectors -a costly exercise as it is estimated that roughly a hundredfold higher photon flux is required. Without reducing the atmospheric losses, or increasing the entanglement efficiency, this implies installing about hundred conventional detector units or using advanced nanowire detectors (about 16 of them) for each polarization direction in the OGS [4]. The space segment is likely not the limiting factor in this experiment.…”