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Register a new userTheoretical investigation of a spectrally pure-state generation from isomorphs of KDP crystal at near-infrared and telecom wavelengths
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Spectrally uncorrelated biphoton state generated from the spontaneous nonlinear optical process is an important resource for quantum information. Currently such spectrally uncorrelated biphoton state can only be prepared from limited kinds of nonlinear media, thus limiting their wavelengths. In order to explore wider wavelength range, here we theoretically study the generation of spectrally uncorrelated biphoton state from 14 isomorphs of potassium dihydrogen phosphate (KDP) crystal. We find that 11 crystals from the `KDP family still maintain similar nonlinear optical properties of KDP, such as KDP, DKDP, ADP, DADP, ADA, DADA, RDA, DRDA, RDP, DRDP and KDA, which satisfy 3 kinds of the group-velocity matching conditions for spectrally uncorrelated biphoton state generation from near-infrared to telecom wavelengths. Based on the uncorrelated biphoton state, we investigate the generation of heralded pure-state single photon by detecting one member of the biphoton state to herald the output of the other. The purity of the heralded single photon is as high as 0.98 without using a narrow-band filter; the Hong-Ou-Mandel interference from independent sources can also achieve a visibility of 98%. This study may provide more and better single-photon sources for quantum information processing at near-infrared and telecom wavelengths.
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We theoretically investigate the preparation of mid-infrared (MIR) spectrally-uncorrelated biphotons from a spontaneous parametric down-conversion process using doped LN crystals, including MgO doped LN, ZnO doped LN, and In2O3 doped ZnLN with doping ratio from 0 to 7 mol%. The tilt angle of the phase-matching function and the corresponding poling period are calculated under type-II, type-I, and type-0 phase-matching conditions. We also calculate the thermal properties of the doped LN crystals and their performance in Hong-Ou-Mandel interference. It is found that the doping ratio has a substantial impact on the group-velocity-matching (GVM) wavelengths. Especially, the GVM2 wavelength of co-doped InZnLN crystal has a tunable range of 678.7 nm, which is much broader than the tunable range of less than 100 nm achieved by the conventional method of adjusting the temperature. It can be concluded that the doping ratio can be utilized as a degree of freedom to manipulate the biphoton state. The spectrally uncorrelated biphotons can be used to prepare pure single-photon source and entangled photon source, which may have promising applications for quantum-enhanced sensing, imaging, and communications at the MIR range.
Highly efficient terahertz (THz) wave sources based on difference frequency generation (DFG) process in nonlinear optical crystals play an important role for the applications of THz wave. In order to find more novel nonlinear crystals, here we theoretically investigate the generation of THz wave using the isomorphs of periodically poled $mathrm{KTiOPO_4}$ (PPKTP), including periodically poled RTP, KTA, RTA and CTA. By solving the cascaded difference frequency coupled wave equations, it is found that the intensities of the THz wave generated from the cascaded difference frequency processes are improved by 5.27, 2.87, 2.82, 3.03, and 2.76 times from the non-cascaded cases for KTP, RTP, KTA, RTA and CTA, respectively. The effects of the crystal absorption, the phase mismatch and the pump intensity are also analyzed in detail. This study might help to provide a stronger THz radiation source based on the nonlinear crystals.
We characterize a periodically poled KTP crystal that produces an entangled, two-mode, squeezed state with orthogonal polarizations, nearly identical, factorizable frequency modes, and few photons in unwanted frequency modes. We focus the pump beam to create a nearly circular joint spectral probability distribution between the two modes. After disentangling the two modes, we observe Hong-Ou-Mandel interference with a raw (background corrected) visibility of 86 % (95 %) when an 8.6 nm bandwidth spectral filter is applied. We measure second order photon correlations of the entangled and disentangled squeezed states with both superconducting nanowire single-photon detectors and photon-number-resolving transition-edge sensors. Both methods agree and verify that the detected modes contain the desired photon number distributions.
Nanofabricated mechanical resonators are gaining significant momentum among potential quantum technologies due to their unique design freedom and independence from naturally occurring resonances. With their functionality being widely detached from material choice, they constitute ideal tools to be used as transducers, i.e. intermediaries between different quantum systems, and as memory elements in conjunction with quantum communication and computing devices. Their capability to host ultra-long lived phonon modes is particularity attractive for non-classical information storage, both for future quantum technologies as well as for fundamental tests of physics. Here we demonstrate such a mechanical quantum memory with an energy decay time of $T_1approx2$ ms, which is controlled through an optical interface engineered to natively operate at telecom wavelengths. We further investigate the coherence of the memory, equivalent to the dephasing $T_2^*$ for qubits, which exhibits a power dependent value between 15 and 112 $mu$s. This demonstration is enabled by a novel optical scheme to create a superposition state of $rvert{0}rangle+rvert{1}rangle$ mechanical excitations, with an arbitrary ratio between the vacuum and single phonon components.
Based on the principles of microwave circuit interferometry we have constructed a Reduced Noise Amplifier (RNA) with power spectral density of phase, as well as amplitude, fluctuations close to -170 dBc/Hz at 1 kHz offset. The RNA has been incorporated with a cryogenic sapphire resonator as a loop oscillator whose noise performance is governed by the Leesons model. Following this model and using the results of in-situ measurements of gain and phase fluctuations of the RNA we inferred noise properties of the oscillator. In particular, for a signal transmitted through the resonator we found that power spectral density of its phase/amplitude fluctuations must be close to -185 dBc/Hz at offsets above 300 Hz. We discuss a few approaches that will allow direct measurements of such low levels of noise.
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