Probing QED and fundamental constants through laser spectroscopy of vibrational transitions in HD+

Abstract

The simplest molecules in nature, molecular hydrogen ions in the form of H2+ and HD+, provide an important benchmark system for tests of quantum electrodynamics in complex forms of matter. Here, we report on such a test based on a frequency measurement of a vibrational overtone transition in HD+ by laser spectroscopy. We find that the theoretical and experimental frequencies are equal to within 0.6(1.1) parts per billion, which represents the most stringent test of molecular theory so far. Our measurement not only confirms the validity of high-order quantum electrodynamics in molecules, but also enables the long predicted determination of the proton-to-electron mass ratio from a molecular system, as well as improved constraints on hypothetical fifth forces and compactified higher dimensions at the molecular scale. With the perspective of comparisons between theory and experiment at the 0.01 part-per-billion level, our work demonstrates the potential of molecular hydrogen ions as a probe of fundamental physical constants and laws.

High-precision spectroscopy of the HD+ molecule at the 1-p.p.b. level

“…level, and a test of molecular QED at the level of 2.7 × 10 −4 , which are the most stringent tests performed so far. Second, it allows us to put new bounds on the existence of hypothetical fifth forces, and put new limits on the compactification radius of higher dimensions, as described in detail in [3,4,12]. Third, the result presented here can be used to obtain a new value the proton-to-electron mass ratio with a precision of 2.9 p.p.b.…”

“…Note that the specified error (within parentheses) does not include the uncertainty of the fundamental constants used. By far the largest contribution is due to the 4.1 × 10 −10 uncertainty of the 2010 Committee on Data for Science and Technology (CODATA) value of μ [16], which translates to a relative frequency uncertainty of 1.5 × 10 −10 (and an absolute frequency uncertainty of 59 kHz) [12].…”

“…Third, the result presented here can be used to obtain a new value the proton-to-electron mass ratio with a precision of 2.9 p.p.b. [12], for the first time from molecular spectroscopy as proposed already four decades ago [5].…”

“…In this article, we present the result of a high-precision frequency measurement of the ro-vibrational transition (v, L):(0, 2)→ (8,3) in the HD + molecule and compare it with state-of-the-art molecular theory to find excellent agreement. From this comparison, we subsequently derive new constraints on the size of effects due to possible new physics (in the form of hypothetical fifth forces or compactified higher dimensions [3,4,12]) in HD + , and we determine a value of μ for the first time from a molecular system [12].…”

High-accuracy deep-UV Ramsey-comb spectroscopy in krypton

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and bound-state QED tests based on precision spectroscopy in atoms, molecules and highly charged ions (see, e.g., [5][6][7][8][9][10]). Moreover, in the pursuit of testing QED ever better, substantial efforts have been made to extract fundamental quantities such as the Rydberg constant R ∞ and the proton charge radius.

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