Expression  may mean a state with single photon, or the coherent state with mean amplitude equal to 1, or state with momentum equal to unity, and so on.
ɛkspɹˈɛʃən mˈeɪ mˈiːn ɐ stˈeɪt wɪð sˈɪŋɡəl fˈoʊtɑːn, ɔːɹ ðə koʊhˈɪɹənt stˈeɪt wɪð mˈiːn ˈæmplɪtˌuːd ˈiːkwəl tə wˈʌn, ɔːɹ stˈeɪt wɪð moʊmˈɛntəm ˈiːkwəl tə jˈuːnɪɾi, ænd sˌoʊ ˈɔn.